ISTART - Revision history

Ftran at 10:20, 27 March 2025

2025-03-27T10:20:20Z

← Older revision		Revision as of 10:20, 27 March 2025
Line 29:		Line 29:
	:Continuation job: "full restart including orbitals and charge prediction".		:Continuation job: "full restart including orbitals and charge prediction".

	:Same as {{TAG\|ISTART}}=2 but in addition a valid {{FILE\|TMPCAR}} file must exist, containing the positions and orbitals at time steps <math>t(N-1)</math> and <math>t(N-2)</math>, which are needed for the ~~orbtial~~ and charge prediction scheme (used for MD-runs).		:Same as {{TAG\|ISTART}}=2 but in addition a valid {{FILE\|TMPCAR}} file must exist, containing the positions and orbitals at time steps <math>t(N-1)</math> and <math>t(N-2)</math>, which are needed for the orbital and charge prediction scheme (used for MD-runs).

	:{{TAG\|ISTART}}=3 is generally not recommended unless an operating system imposes a serious restriction on the CPU time per job: if you continue with {{TAG\|ISTART}}=1 or 2, a relatively large number of electronic iterations might be necessary to reach convergence of the orbitals in the second and third molecular-dynamics steps. {{TAG\|ISTART}}=3 therefore saves time and is important if a molecular-dynamics run is split into very small pieces (e.g., {{TAG\|NSW}}<10).		:{{TAG\|ISTART}}=3 is generally not recommended unless an operating system imposes a serious restriction on the CPU time per job: if you continue with {{TAG\|ISTART}}=1 or 2, a relatively large number of electronic iterations might be necessary to reach convergence of the orbitals in the second and third molecular-dynamics steps. {{TAG\|ISTART}}=3 therefore saves time and is important if a molecular-dynamics run is split into very small pieces (e.g., {{TAG\|NSW}}<10).

Csheldon at 09:44, 9 September 2024

2024-09-09T09:44:43Z

← Older revision		Revision as of 09:44, 9 September 2024
Line 21:		Line 21:

	:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.		:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.
	{{NB\|mind\| Due to [[Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy ~~cutoff~~ (unless absolute convergence with respect to the basis set is achieved!).\|:}}		{{NB\|mind\| Due to [[Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!).\|:}}
	:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Volume relaxation\|volume relaxations]]).		:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Volume relaxation\|volume relaxations]]).

Csheldon at 09:43, 9 September 2024

2024-09-09T09:43:58Z

← Older revision		Revision as of 09:43, 9 September 2024
Line 21:		Line 21:

	:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.		:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.
	{{NB\|mind\| Due to [[Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy ~~cut-off~~ (unless absolute convergence with respect to the basis set is achieved!).\|:}}		{{NB\|mind\| Due to [[Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cutoff (unless absolute convergence with respect to the basis set is achieved!).\|:}}
	:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Volume relaxation\|volume relaxations]]).		:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Volume relaxation\|volume relaxations]]).

Csheldon at 09:30, 9 September 2024

2024-09-09T09:30:54Z

← Older revision		Revision as of 09:30, 9 September 2024
Line 9:		Line 9:
	:Continuation job: "restart with constant energy cut-off". Orbitals are read from the {{FILE\|WAVECAR}} file (usage is restricted in the parallel version). The set of plane waves will be redefined and re-padded according to the new cell size/shape ({{FILE\|POSCAR}}) and the new plane wave cut-off ({{FILE\|INCAR}}). These values might differ from the old values, that are stored in the {{FILE\|WAVECAR}} file. If the {{FILE\|WAVECAR}} file is missing or if the {{FILE\|WAVECAR}} file contains an inappropriate number of bands and/or k-points the flag {{TAG\|ISTART}} will revert to {{TAG\|ISTART}}=0 (see above).		:Continuation job: "restart with constant energy cut-off". Orbitals are read from the {{FILE\|WAVECAR}} file (usage is restricted in the parallel version). The set of plane waves will be redefined and re-padded according to the new cell size/shape ({{FILE\|POSCAR}}) and the new plane wave cut-off ({{FILE\|INCAR}}). These values might differ from the old values, that are stored in the {{FILE\|WAVECAR}} file. If the {{FILE\|WAVECAR}} file is missing or if the {{FILE\|WAVECAR}} file contains an inappropriate number of bands and/or k-points the flag {{TAG\|ISTART}} will revert to {{TAG\|ISTART}}=0 (see above).

	:The usage of {{TAG\|ISTART}}=1 is recommended if the size/shape of the supercell (see section on [[~~Energy vs volume~~ Volume ~~relaxations and Pulay stress~~\|volume ~~versus energy~~]]) or the cut-off energy changed with respect to the last run and if one wishes to redefine the set of plane waves according to a new setting.		:The usage of {{TAG\|ISTART}}=1 is recommended if the size/shape of the supercell (see section on [[Volume relaxation\|volume relaxations]]) or the cut-off energy changed with respect to the last run and if one wishes to redefine the set of plane waves according to a new setting.

	:{{TAG\|ISTART}}=1 is the usual setting for convergence tests with respect to the cut-off energy and for all jobs where the volume/cell-shape varies (e.g. to calculate binding energy curves looping over a set of volumes).		:{{TAG\|ISTART}}=1 is the usual setting for convergence tests with respect to the cut-off energy and for all jobs where the volume/cell-shape varies (e.g. to calculate binding energy curves looping over a set of volumes).
Line 21:		Line 21:

	:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.		:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.
	{{NB\|mind\| Due to [[~~Energy vs volume Volume relaxations and~~ Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!).\|:}}		{{NB\|mind\| Due to [[Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!).\|:}}
	:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[~~Energy vs volume~~ Volume ~~relaxations and Pulay stress~~\|volume ~~versus energy~~]]).		:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Volume relaxation\|volume relaxations]]).

	:There is only one exception to this general rule: all volume/cell shape relaxation algorithms implemented in VASP work with a constant basis set, so continuing such jobs requires to set {{TAG\|ISTART}}=2 to get a 'consistent restart' with respect to the previous runs (see section [[~~Energy vs~~ volume ~~Volume~~ relaxations ~~and~~ Pulay stress\|~~volume versus energy~~]])!		:There is only one exception to this general rule: all volume/cell shape relaxation algorithms implemented in VASP work with a constant basis set, so continuing such jobs requires to set {{TAG\|ISTART}}=2 to get a 'consistent restart' with respect to the previous runs (see section [[Volume relaxation\|volume relaxations]])! This menas that that number of plane waves is consistent with the previous run but the energy cut-off is not (see section [[Pulay stress\|Pulay stress]]).

	*{{TAG\|ISTART}}=3		*{{TAG\|ISTART}}=3

Karsai at 14:24, 8 April 2022

2022-04-08T14:24:06Z

← Older revision		Revision as of 14:24, 8 April 2022
Line 39:		Line 39:
	----		----

	[[Category:INCAR]][[Category:Electronic minimization]]		[[Category:INCAR tag]][[Category:Electronic minimization]]

Huebsch at 12:09, 6 April 2022

2022-04-06T12:09:14Z

← Older revision		Revision as of 12:09, 6 April 2022
Line 21:		Line 21:

	:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.		:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.
			{{NB\|mind\| Due to [[Energy vs volume Volume relaxations and Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!).\|:}}
	~~:'''Mind''':~~ Due to ~~Pullay~~ stresses, there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!). If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]]).		:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]]).

	:There is only one exception to this general rule: all volume/cell shape relaxation algorithms implemented in VASP work with a constant basis set, so continuing such jobs requires to set {{TAG\|ISTART}}=2 to get a 'consistent restart' with respect to the previous runs (see section [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]])!		:There is only one exception to this general rule: all volume/cell shape relaxation algorithms implemented in VASP work with a constant basis set, so continuing such jobs requires to set {{TAG\|ISTART}}=2 to get a 'consistent restart' with respect to the previous runs (see section [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]])!
Line 31:		Line 31:
	:Same as {{TAG\|ISTART}}=2 but in addition a valid {{FILE\|TMPCAR}} file must exist, containing the positions and orbitals at time steps <math>t(N-1)</math> and <math>t(N-2)</math>, which are needed for the orbtial and charge prediction scheme (used for MD-runs).		:Same as {{TAG\|ISTART}}=2 but in addition a valid {{FILE\|TMPCAR}} file must exist, containing the positions and orbitals at time steps <math>t(N-1)</math> and <math>t(N-2)</math>, which are needed for the orbtial and charge prediction scheme (used for MD-runs).

	:{{TAG\|ISTART}}=3 is generally not recommended unless an operating system imposes serious restriction on the CPU time per job: if you continue with {{TAG\|ISTART}}=1 or 2, a relatively large number of electronic iterations might be necessary to reach convergence of the orbitals in the second and third MD-steps. {{TAG\|ISTART}}=3 therefore saves time and is important if a MD-run is split into very small pieces (e.g. {{TAG\|NSW}}<10).		:{{TAG\|ISTART}}=3 is generally not recommended unless an operating system imposes a serious restriction on the CPU time per job: if you continue with {{TAG\|ISTART}}=1 or 2, a relatively large number of electronic iterations might be necessary to reach convergence of the orbitals in the second and third molecular-dynamics steps. {{TAG\|ISTART}}=3 therefore saves time and is important if a molecular-dynamics run is split into very small pieces (e.g., {{TAG\|NSW}}<10).

	:Nevertheless, we have found that it is safer to restart the orbital prediction after 100 to 200 steps. If {{TAG\|NSW}}>30, {{TAG\|ISTART}}=1 or 2 is strongly recommended.		:Nevertheless, we have found that it is safer to restart the orbital prediction after 100 to 200 steps. If {{TAG\|NSW}}>30, {{TAG\|ISTART}}=1 or 2 is strongly recommended.
			{{NB\|mind\| If {{TAG\|ISTART}}{{=}}3, a non-existing {{FILE\|WAVECAR}} or {{FILE\|TMPCAR}} file or any inconsistency of input data will immediately stop execution.\|:}}
	~~:'''Mind''':~~ If {{TAG\|ISTART}}=3, a non-existing {{FILE\|WAVECAR}} or {{FILE\|TMPCAR}} file or any inconsistency of input data will immediately stop execution.

	{{sc\|ISTART\|Examples\|Examples that use this tag}}		{{sc\|ISTART\|Examples\|Examples that use this tag}}
	----		----

	[[Category:INCAR]][[Category:Electronic ~~Minimization]][[Category:Electronic Minimization Methods~~]]		[[Category:INCAR]][[Category:Electronic minimization]]

Schlipf at 10:15, 14 January 2020

2020-01-14T10:15:09Z

← Older revision		Revision as of 10:15, 14 January 2020
Line 9:		Line 9:
	:Continuation job: "restart with constant energy cut-off". Orbitals are read from the {{FILE\|WAVECAR}} file (usage is restricted in the parallel version). The set of plane waves will be redefined and re-padded according to the new cell size/shape ({{FILE\|POSCAR}}) and the new plane wave cut-off ({{FILE\|INCAR}}). These values might differ from the old values, that are stored in the {{FILE\|WAVECAR}} file. If the {{FILE\|WAVECAR}} file is missing or if the {{FILE\|WAVECAR}} file contains an inappropriate number of bands and/or k-points the flag {{TAG\|ISTART}} will revert to {{TAG\|ISTART}}=0 (see above).		:Continuation job: "restart with constant energy cut-off". Orbitals are read from the {{FILE\|WAVECAR}} file (usage is restricted in the parallel version). The set of plane waves will be redefined and re-padded according to the new cell size/shape ({{FILE\|POSCAR}}) and the new plane wave cut-off ({{FILE\|INCAR}}). These values might differ from the old values, that are stored in the {{FILE\|WAVECAR}} file. If the {{FILE\|WAVECAR}} file is missing or if the {{FILE\|WAVECAR}} file contains an inappropriate number of bands and/or k-points the flag {{TAG\|ISTART}} will revert to {{TAG\|ISTART}}=0 (see above).

	:The usage of {{TAG\|ISTART}}=1 is recommended if the size/shape of the supercell (see section on [[Pulay stress\|volume ~~relaxation~~]]) or the cut-off energy changed with respect to the last run and if one wishes to redefine the set of plane waves according to a new setting.		:The usage of {{TAG\|ISTART}}=1 is recommended if the size/shape of the supercell (see section on [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]]) or the cut-off energy changed with respect to the last run and if one wishes to redefine the set of plane waves according to a new setting.

	:{{TAG\|ISTART}}=1 is the usual setting for convergence tests with respect to the cut-off energy and for all jobs where the volume/cell-shape varies (e.g. to calculate binding energy curves looping over a set of volumes).		:{{TAG\|ISTART}}=1 is the usual setting for convergence tests with respect to the cut-off energy and for all jobs where the volume/cell-shape varies (e.g. to calculate binding energy curves looping over a set of volumes).

Schlipf at 10:14, 14 January 2020

2020-01-14T10:14:50Z

← Older revision		Revision as of 10:14, 14 January 2020
Line 22:		Line 22:
	:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.		:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.

	:'''Mind''': Due to Pullay stresses, there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!). If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Pulay stress\|volume versus energy]]).		:'''Mind''': Due to Pullay stresses, there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!). If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]]).

	:There is only one exception to this general rule: all volume/cell shape relaxation algorithms implemented in VASP work with a constant basis set, so continuing such jobs requires to set {{TAG\|ISTART}}=2 to get a 'consistent restart' with respect to the previous runs (see section ~~\ref{pullay}~~)!		:There is only one exception to this general rule: all volume/cell shape relaxation algorithms implemented in VASP work with a constant basis set, so continuing such jobs requires to set {{TAG\|ISTART}}=2 to get a 'consistent restart' with respect to the previous runs (see section [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]])!

	*{{TAG\|ISTART}}=3		*{{TAG\|ISTART}}=3

Karsai at 10:41, 11 April 2019

2019-04-11T10:41:18Z

← Older revision		Revision as of 10:41, 11 April 2019
Line 39:		Line 39:
	{{sc\|ISTART\|Examples\|Examples that use this tag}}		{{sc\|ISTART\|Examples\|Examples that use this tag}}
	----		----
	~~[[The_VASP_Manual\|Contents]]~~

	[[Category:INCAR]][[Category:Electronic Minimization]][[Category:Electronic Minimization Methods]]		[[Category:INCAR]][[Category:Electronic Minimization]][[Category:Electronic Minimization Methods]]

Karsai at 11:07, 7 March 2019

2019-03-07T11:07:17Z

← Older revision		Revision as of 11:07, 7 March 2019
Line 41:		Line 41:
	[[The_VASP_Manual\|Contents]]		[[The_VASP_Manual\|Contents]]

	[[Category:INCAR]][[Category:Electronic Minimization Methods]]		[[Category:INCAR]][[Category:Electronic Minimization]][[Category:Electronic Minimization Methods]]

← Older revision		Revision as of 09:44, 9 September 2024
Line 21:		Line 21:

	:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.		:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.
	{{NB\|mind\| Due to [[Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy ~~cutoff~~ (unless absolute convergence with respect to the basis set is achieved!).\|:}}		{{NB\|mind\| Due to [[Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!).\|:}}
	:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Volume relaxation\|volume relaxations]]).		:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Volume relaxation\|volume relaxations]]).

← Older revision		Revision as of 09:43, 9 September 2024
Line 21:		Line 21:

	:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.		:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.
	{{NB\|mind\| Due to [[Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy ~~cut-off~~ (unless absolute convergence with respect to the basis set is achieved!).\|:}}		{{NB\|mind\| Due to [[Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cutoff (unless absolute convergence with respect to the basis set is achieved!).\|:}}
	:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Volume relaxation\|volume relaxations]]).		:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Volume relaxation\|volume relaxations]]).

← Older revision		Revision as of 09:30, 9 September 2024
Line 9:		Line 9:
	:Continuation job: "restart with constant energy cut-off". Orbitals are read from the {{FILE\|WAVECAR}} file (usage is restricted in the parallel version). The set of plane waves will be redefined and re-padded according to the new cell size/shape ({{FILE\|POSCAR}}) and the new plane wave cut-off ({{FILE\|INCAR}}). These values might differ from the old values, that are stored in the {{FILE\|WAVECAR}} file. If the {{FILE\|WAVECAR}} file is missing or if the {{FILE\|WAVECAR}} file contains an inappropriate number of bands and/or k-points the flag {{TAG\|ISTART}} will revert to {{TAG\|ISTART}}=0 (see above).		:Continuation job: "restart with constant energy cut-off". Orbitals are read from the {{FILE\|WAVECAR}} file (usage is restricted in the parallel version). The set of plane waves will be redefined and re-padded according to the new cell size/shape ({{FILE\|POSCAR}}) and the new plane wave cut-off ({{FILE\|INCAR}}). These values might differ from the old values, that are stored in the {{FILE\|WAVECAR}} file. If the {{FILE\|WAVECAR}} file is missing or if the {{FILE\|WAVECAR}} file contains an inappropriate number of bands and/or k-points the flag {{TAG\|ISTART}} will revert to {{TAG\|ISTART}}=0 (see above).

	:The usage of {{TAG\|ISTART}}=1 is recommended if the size/shape of the supercell (see section on [[~~Energy vs volume~~ Volume ~~relaxations and Pulay stress~~\|volume ~~versus energy~~]]) or the cut-off energy changed with respect to the last run and if one wishes to redefine the set of plane waves according to a new setting.		:The usage of {{TAG\|ISTART}}=1 is recommended if the size/shape of the supercell (see section on [[Volume relaxation\|volume relaxations]]) or the cut-off energy changed with respect to the last run and if one wishes to redefine the set of plane waves according to a new setting.

	:{{TAG\|ISTART}}=1 is the usual setting for convergence tests with respect to the cut-off energy and for all jobs where the volume/cell-shape varies (e.g. to calculate binding energy curves looping over a set of volumes).		:{{TAG\|ISTART}}=1 is the usual setting for convergence tests with respect to the cut-off energy and for all jobs where the volume/cell-shape varies (e.g. to calculate binding energy curves looping over a set of volumes).
Line 21:		Line 21:

	:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.		:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.
	{{NB\|mind\| Due to [[~~Energy vs volume Volume relaxations and~~ Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!).\|:}}		{{NB\|mind\| Due to [[Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!).\|:}}
	:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[~~Energy vs volume~~ Volume ~~relaxations and Pulay stress~~\|volume ~~versus energy~~]]).		:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Volume relaxation\|volume relaxations]]).

	:There is only one exception to this general rule: all volume/cell shape relaxation algorithms implemented in VASP work with a constant basis set, so continuing such jobs requires to set {{TAG\|ISTART}}=2 to get a 'consistent restart' with respect to the previous runs (see section [[~~Energy vs~~ volume ~~Volume~~ relaxations ~~and~~ Pulay stress\|~~volume versus energy~~]])!		:There is only one exception to this general rule: all volume/cell shape relaxation algorithms implemented in VASP work with a constant basis set, so continuing such jobs requires to set {{TAG\|ISTART}}=2 to get a 'consistent restart' with respect to the previous runs (see section [[Volume relaxation\|volume relaxations]])! This menas that that number of plane waves is consistent with the previous run but the energy cut-off is not (see section [[Pulay stress\|Pulay stress]]).

	*{{TAG\|ISTART}}=3		*{{TAG\|ISTART}}=3

← Older revision		Revision as of 12:09, 6 April 2022
Line 21:		Line 21:

	:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.		:{{TAG\|ISTART}}=2 is usually used if one wishes to restart with the same basis set used in the previous run.
			{{NB\|mind\| Due to [[Energy vs volume Volume relaxations and Pulay stress\|Pulay stresses]], there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!).\|:}}
	~~:'''Mind''':~~ Due to ~~Pullay~~ stresses, there is a difference between evaluating the equilibrium volume with a constant basis set and a constant energy cut-off (unless absolute convergence with respect to the basis set is achieved!). If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]]).		:If you are looking for the equilibrium volume, calculations with a constant energy cut-off are preferable to calculations with a constant basis set, therefore always restart with {{TAG\|ISTART}}=1 unless you really know what you are looking for (see the section on [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]]).

	:There is only one exception to this general rule: all volume/cell shape relaxation algorithms implemented in VASP work with a constant basis set, so continuing such jobs requires to set {{TAG\|ISTART}}=2 to get a 'consistent restart' with respect to the previous runs (see section [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]])!		:There is only one exception to this general rule: all volume/cell shape relaxation algorithms implemented in VASP work with a constant basis set, so continuing such jobs requires to set {{TAG\|ISTART}}=2 to get a 'consistent restart' with respect to the previous runs (see section [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]])!
Line 31:		Line 31:
	:Same as {{TAG\|ISTART}}=2 but in addition a valid {{FILE\|TMPCAR}} file must exist, containing the positions and orbitals at time steps <math>t(N-1)</math> and <math>t(N-2)</math>, which are needed for the orbtial and charge prediction scheme (used for MD-runs).		:Same as {{TAG\|ISTART}}=2 but in addition a valid {{FILE\|TMPCAR}} file must exist, containing the positions and orbitals at time steps <math>t(N-1)</math> and <math>t(N-2)</math>, which are needed for the orbtial and charge prediction scheme (used for MD-runs).

	:{{TAG\|ISTART}}=3 is generally not recommended unless an operating system imposes serious restriction on the CPU time per job: if you continue with {{TAG\|ISTART}}=1 or 2, a relatively large number of electronic iterations might be necessary to reach convergence of the orbitals in the second and third MD-steps. {{TAG\|ISTART}}=3 therefore saves time and is important if a MD-run is split into very small pieces (e.g. {{TAG\|NSW}}<10).		:{{TAG\|ISTART}}=3 is generally not recommended unless an operating system imposes a serious restriction on the CPU time per job: if you continue with {{TAG\|ISTART}}=1 or 2, a relatively large number of electronic iterations might be necessary to reach convergence of the orbitals in the second and third molecular-dynamics steps. {{TAG\|ISTART}}=3 therefore saves time and is important if a molecular-dynamics run is split into very small pieces (e.g., {{TAG\|NSW}}<10).

	:Nevertheless, we have found that it is safer to restart the orbital prediction after 100 to 200 steps. If {{TAG\|NSW}}>30, {{TAG\|ISTART}}=1 or 2 is strongly recommended.		:Nevertheless, we have found that it is safer to restart the orbital prediction after 100 to 200 steps. If {{TAG\|NSW}}>30, {{TAG\|ISTART}}=1 or 2 is strongly recommended.
			{{NB\|mind\| If {{TAG\|ISTART}}{{=}}3, a non-existing {{FILE\|WAVECAR}} or {{FILE\|TMPCAR}} file or any inconsistency of input data will immediately stop execution.\|:}}
	~~:'''Mind''':~~ If {{TAG\|ISTART}}=3, a non-existing {{FILE\|WAVECAR}} or {{FILE\|TMPCAR}} file or any inconsistency of input data will immediately stop execution.

	{{sc\|ISTART\|Examples\|Examples that use this tag}}		{{sc\|ISTART\|Examples\|Examples that use this tag}}
	----		----

	[[Category:INCAR]][[Category:Electronic ~~Minimization]][[Category:Electronic Minimization Methods~~]]		[[Category:INCAR]][[Category:Electronic minimization]]

← Older revision		Revision as of 10:15, 14 January 2020
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	:Continuation job: "restart with constant energy cut-off". Orbitals are read from the {{FILE\|WAVECAR}} file (usage is restricted in the parallel version). The set of plane waves will be redefined and re-padded according to the new cell size/shape ({{FILE\|POSCAR}}) and the new plane wave cut-off ({{FILE\|INCAR}}). These values might differ from the old values, that are stored in the {{FILE\|WAVECAR}} file. If the {{FILE\|WAVECAR}} file is missing or if the {{FILE\|WAVECAR}} file contains an inappropriate number of bands and/or k-points the flag {{TAG\|ISTART}} will revert to {{TAG\|ISTART}}=0 (see above).		:Continuation job: "restart with constant energy cut-off". Orbitals are read from the {{FILE\|WAVECAR}} file (usage is restricted in the parallel version). The set of plane waves will be redefined and re-padded according to the new cell size/shape ({{FILE\|POSCAR}}) and the new plane wave cut-off ({{FILE\|INCAR}}). These values might differ from the old values, that are stored in the {{FILE\|WAVECAR}} file. If the {{FILE\|WAVECAR}} file is missing or if the {{FILE\|WAVECAR}} file contains an inappropriate number of bands and/or k-points the flag {{TAG\|ISTART}} will revert to {{TAG\|ISTART}}=0 (see above).

	:The usage of {{TAG\|ISTART}}=1 is recommended if the size/shape of the supercell (see section on [[Pulay stress\|volume ~~relaxation~~]]) or the cut-off energy changed with respect to the last run and if one wishes to redefine the set of plane waves according to a new setting.		:The usage of {{TAG\|ISTART}}=1 is recommended if the size/shape of the supercell (see section on [[Energy vs volume Volume relaxations and Pulay stress\|volume versus energy]]) or the cut-off energy changed with respect to the last run and if one wishes to redefine the set of plane waves according to a new setting.

	:{{TAG\|ISTART}}=1 is the usual setting for convergence tests with respect to the cut-off energy and for all jobs where the volume/cell-shape varies (e.g. to calculate binding energy curves looping over a set of volumes).		:{{TAG\|ISTART}}=1 is the usual setting for convergence tests with respect to the cut-off energy and for all jobs where the volume/cell-shape varies (e.g. to calculate binding energy curves looping over a set of volumes).