ENCUTGW - Revision history

Kaltakm at 14:07, 24 April 2023

2023-04-24T14:07:20Z

← Older revision		Revision as of 14:07, 24 April 2023
Line 21:		Line 21:

	Our experience suggests that choosing {{TAG\|ENCUTGW}}= 2/3 {{TAG\|ENCUT}} yields reasonable results at fairly modest computational cost, although, the response function contains contributions up to twice the plane wave cutoff <math>G_{\rm cut}</math>, see {{TAG\|ALGO}} tag. Furthermore, RPA correlation energies are reported using an internal extrapolation of the correlation energy by varying the value of {{TAG\|ENCUTGW}} inside VASP between the largest value given in the {{TAG\|INCAR}} file and smaller values {{cite\|harl:prb:08}}. Mind: The extrapolated value is only reliable, if {{TAG\|ENCUTGW}} is smaller then {{TAG\|ENCUT}}. The cutoff extrapolation with respect to {{TAG\|ENCUTGW}} would be precise if the plane wave basis for the orbitals were infinite. Again, the VASP defaults yield very reasonable values for the extrapolated correlation energy. In fact, it is unwise to increase {{TAG\|ENCUTGW}} only, without increasing {{TAG\|ENCUT}}. To converge RPA correlation energies, simply increase {{TAG\|ENCUT}} and the number of orbitals, and use the VASP default for {{TAG\|ENCUTGW}}.		Our experience suggests that choosing {{TAG\|ENCUTGW}}= 2/3 {{TAG\|ENCUT}} yields reasonable results at fairly modest computational cost, although, the response function contains contributions up to twice the plane wave cutoff <math>G_{\rm cut}</math>, see {{TAG\|ALGO}} tag. Furthermore, RPA correlation energies are reported using an internal extrapolation of the correlation energy by varying the value of {{TAG\|ENCUTGW}} inside VASP between the largest value given in the {{TAG\|INCAR}} file and smaller values {{cite\|harl:prb:08}}. Mind: The extrapolated value is only reliable, if {{TAG\|ENCUTGW}} is smaller then {{TAG\|ENCUT}}. The cutoff extrapolation with respect to {{TAG\|ENCUTGW}} would be precise if the plane wave basis for the orbitals were infinite. Again, the VASP defaults yield very reasonable values for the extrapolated correlation energy. In fact, it is unwise to increase {{TAG\|ENCUTGW}} only, without increasing {{TAG\|ENCUT}}. To converge RPA correlation energies, simply increase {{TAG\|ENCUT}} and the number of orbitals, and use the VASP default for {{TAG\|ENCUTGW}}.
			{{NB\|mind\|More details on how the infinite basis set limit is extrapolated in RPA/ACFDT can be found [[ACFDT/RPA_calculations#Basis_set_convergence\|here]].}}
	For quasiparticle (QP) bandgaps, it is sometimes possible to set {{TAG\|ENCUTGW}} to values between 150 to 200 eV, and even 100 eV can yield		For quasiparticle (QP) bandgaps, it is sometimes possible to set {{TAG\|ENCUTGW}} to values between 150 to 200 eV, and even 100 eV can yield
	gaps that are accurate to within a few tens of an eV for main group elements. Be aware, however, that the absolute values of the QP energies depend inverse proportionally on the number of plane waves. Thus, the convergence of absolute QP energies is very slow, although QP gaps might seem converged.		gaps that are accurate to within a few tens of an eV for main group elements. Be aware, however, that the absolute values of the QP energies depend inverse proportionally on the number of plane waves. Thus, the convergence of absolute QP energies is very slow, although QP gaps might seem converged.
Line 32:		Line 32:

	This procedure can be carried out using few k points. Other commonly applied methods can yield less accurate results and are not considered to be reliable.		This procedure can be carried out using few k points. Other commonly applied methods can yield less accurate results and are not considered to be reliable.


	== FFT grid and {{TAG\|PRECFOCK}} ==		== FFT grid and {{TAG\|PRECFOCK}} ==

Kaltakm at 13:48, 6 March 2023

2023-03-06T13:48:10Z

← Older revision		Revision as of 13:48, 6 March 2023
Line 43:		Line 43:
	{{TAG\|ENCUTGWSOFT}},		{{TAG\|ENCUTGWSOFT}},
	{{TAG\|GW calculations}},		{{TAG\|GW calculations}},
	~~{{TAG\|~~ACFDT/~~RPA calculations}}~~		[[ACFDT/RPA_calculations#Basis_set_convergence\|Basis set convergence]]

	{{sc\|ENCUTGW\|Examples\|Examples that use this tag}}		{{sc\|ENCUTGW\|Examples\|Examples that use this tag}}

Huebsch at 10:00, 19 July 2022

2022-07-19T10:00:20Z

← Older revision		Revision as of 10:00, 19 July 2022
Line 55:		Line 55:
	----		----

	[[Category:INCAR tag]][[Category:Many-~~Body Perturbation Theory~~]][[Category:GW]]		[[Category:INCAR tag]][[Category:Many-body perturbation theory]][[Category:GW]]

Karsai at 14:12, 8 April 2022

2022-04-08T14:12:59Z

← Older revision		Revision as of 14:12, 8 April 2022
Line 38:		Line 38:
	QP shifts are usually not very sensitive to the setting of {{TAG\|PRECFOCK}} and therefore there is no harm in setting {{TAG\|PRECFOCK}} = ''fast''), whereas for RPA calculations we recommend to set {{TAG\|PRECFOCK}} = ''normal'' to avoid numerical errors.		QP shifts are usually not very sensitive to the setting of {{TAG\|PRECFOCK}} and therefore there is no harm in setting {{TAG\|PRECFOCK}} = ''fast''), whereas for RPA calculations we recommend to set {{TAG\|PRECFOCK}} = ''normal'' to avoid numerical errors.

	== Related ~~Tags~~ and ~~Sections~~ ==		== Related tags and articles ==
	{{TAG\|PRECFOCK}},		{{TAG\|PRECFOCK}},
	{{TAG\|ENCUT}},		{{TAG\|ENCUT}},
Line 54:		Line 54:

	----		----
	~~[[The_VASP_Manual\|Contents]]~~

	[[Category:INCAR]][[Category:Many-Body Perturbation Theory]][[Category:GW]]		[[Category:INCAR tag]][[Category:Many-Body Perturbation Theory]][[Category:GW]]

Huebsch at 02:38, 27 August 2021

2021-08-27T02:38:57Z

← Older revision		Revision as of 02:38, 27 August 2021
Line 2:		Line 2:


	Description: The tag {{TAG\|ENCUTGW}} sets the energy cutoff for response function. It controls the basis set for the response functions		Description: The tag {{TAG\|ENCUTGW}} sets the energy cutoff for the response function. It controls the basis set for the response functions
	in exactly the same manner as {{TAG\|ENCUT}} does for the orbitals.		in exactly the same manner as {{TAG\|ENCUT}} does for the orbitals.

Line 9:		Line 9:

	----		----
	In GW and RPA calculations, storing and manipulating the response function dominates the computational work load:		In GW and random-phase-approximation (RPA) calculations, storing and manipulating the response function dominates the computational work load:

	<math>\chi_{{\mathbf{q}}}^0 ({\mathbf{G}}, {\mathbf{G}}', \omega)=\frac{1}{\Omega} \sum_{n,n',{\mathbf{k}}}2 w_{{\mathbf{k}}}		<math>\chi_{{\mathbf{q}}}^0 ({\mathbf{G}}, {\mathbf{G}}', \omega)=\frac{1}{\Omega} \sum_{n,n',{\mathbf{k}}}2 w_{{\mathbf{k}}}
Line 20:		Line 20:
	the response function <math>\chi_{{\mathbf{q}}}^0 ({\mathbf{G}}, {\mathbf{G}}', \omega)</math>.		the response function <math>\chi_{{\mathbf{q}}}^0 ({\mathbf{G}}, {\mathbf{G}}', \omega)</math>.

	Our experience suggests that choosing {{TAG\|ENCUTGW}}= 2/3 {{TAG\|ENCUT}} yields		Our experience suggests that choosing {{TAG\|ENCUTGW}}= 2/3 {{TAG\|ENCUT}} yields reasonable results at fairly modest computational cost, although, the response function contains contributions up to twice the plane wave cutoff <math>G_{\rm cut}</math>, see {{TAG\|ALGO}} tag. Furthermore, RPA correlation energies are reported using an internal extrapolation of the correlation energy by varying the value of {{TAG\|ENCUTGW}} inside VASP between the largest value given in the {{TAG\|INCAR}} file and smaller values {{cite\|harl:prb:08}}. Mind: The extrapolated value is only reliable, if {{TAG\|ENCUTGW}} is smaller then {{TAG\|ENCUT}}. The cutoff extrapolation with respect to {{TAG\|ENCUTGW}} would be precise if the plane wave basis for the orbitals were infinite. Again, the VASP defaults yield very reasonable values for the extrapolated correlation energy. In fact, it is unwise to increase {{TAG\|ENCUTGW}} only, without increasing {{TAG\|ENCUT}}. To converge RPA correlation energies, simply increase {{TAG\|ENCUT}} and the number of orbitals, and use the VASP default for {{TAG\|ENCUTGW}}.
	reasonable results at fairly modest computational cost, although, the response function
	contains contributions up to twice the plane wave cutoff <math>G_{\rm cut}</math>
	(see {{TAG\|ALGO}}).
	Furthermore, RPA correlation energies are reported using an internal extrapolation of the correlation
	energy by varying {{TAG\|ENCUTGW}} ~~internally (~~inside VASP) between the largest value given in the INCAR
	file and smaller values ~~<ref name="~~harl:08~~"/>~~. The extrapolated value is only reliable, if
	{{TAG\|ENCUTGW}} is smaller then {{TAG\|ENCUT}} ~~(the~~ cutoff extrapolation with respect to {{TAG\|ENCUTGW}}
	would be ~~very~~ precise, if the plane wave basis for the orbitals were infinite).
	Again the VASP defaults yield very reasonable values for the extrapolated correlation
	energy. In fact, it is unwise to increase {{TAG\|ENCUTGW}} only, without increasing {{TAG\|ENCUT}} .
	To converge RPA correlation energies, simply increase {{TAG\|ENCUT}} and the number
	of orbitals, and use the VASP default for {{TAG\|ENCUTGW}}.

	For QP ~~gaps~~, it is sometimes possible to set {{TAG\|ENCUTGW}}		For quasiparticle (QP) bandgaps, it is sometimes possible to set {{TAG\|ENCUTGW}} to values between 150 to 200 eV, and even 100 eV can yield
	to values between 150 to 200 eV, and even 100 eV can yield		gaps that are accurate to within a few tens of an eV for main group elements. Be aware, however, that the absolute values of the QP energies depend inverse proportionally on the number of plane waves. Thus, the convergence of absolute QP energies is very slow, although QP gaps might seem converged.
	gaps that are accurate to within a few tens of an eV for main group elements.
	Be aware, however, that the absolute values of the QP energies
	depend inverse proportionally on the number of plane waves. Thus
	convergence of absolute QP energies is ~~always~~ very slow, although QP gaps
	might seem converged.

	The recommended procedure to obtain accurate QP energies is discussed in the reference below.		The recommended procedure to obtain accurate QP energies is discussed in the reference below. Specifically, for reference type calculations we recommend the following procedure:
	Specifically, for reference type calculations we recommend the following procedure:

	* ~~use~~ the default for ENCUTGW, or even decrease ENCUTGW to half the value of ENCUT.		* Use the default for {{TAG\|ENCUTGW}}, or even decrease {{TAG\|ENCUTGW}} to half the value of {{TAG\|ENCUT}}.
	* Calculate all orbitals that the plane wave basis set allows to calculate. This number can be determined by searching for "maximum number of plane-waves" in the ~~groundstate~~ DFT OUTCAR file, and setting {{TAG\|NBANDS}} to this value.		* Calculate all orbitals that the plane-wave basis set allows to calculate. This number can be determined by searching for "maximum number of plane-waves" in the ground-state DFT {{TAG\|OUTCAR}} file, and setting {{TAG\|NBANDS}} to this value.
	* Increase ENCUT systematically and plot the QP energies versus the number of plane wave coefficients (which equals the number of orbitals). This means ENCUTGW and NBANDS increase as ENCUT increases.		* Increase {{TAG\|ENCUT}} systematically and plot the QP energies versus the number of plane-wave coefficients, which equals the number of orbitals. This means {{TAG\|ENCUTGW}} and {{TAG\|NBANDS}} increase as {{TAG\|ENCUT}} increases.

	This procedure can be carried out using few k-points. Other commonly applied methods can yield less accurate results and are not considered		This procedure can be carried out using few k points. Other commonly applied methods can yield less accurate results and are not considered to be reliable.
	to be reliable.


	== FFT grid and {{TAG\|PRECFOCK}} ==		== FFT grid and {{TAG\|PRECFOCK}} ==
	The ~~flag~~ {{TAG\|PRECFOCK}} determines the FFT grid in all GW (and Hartree-Fock) related routines.		The {{TAG\|PRECFOCK}} tag determines the fast Fourier transformation (FFT) grid in all GW (and Hartree-Fock) related routines. For small systems, the computational time is often dominated by FFT operations. Therefore, the {{TAG\|PRECFOCK}} tag can have a significant impact on the compute time for QP calculations. For large systems, the FFT's usually do not dominate the computational workload, and savings are expected to be small for {{TAG\|PRECFOCK}} = ''fast''.
	For small systems ~~(which are~~ often dominated by FFT operations),		QP shifts are usually not very sensitive to the setting of {{TAG\|PRECFOCK}} and therefore there is no harm in setting {{TAG\|PRECFOCK}} = ''fast''), whereas for RPA calculations we recommend to set {{TAG\|PRECFOCK}} = ''normal'' to avoid numerical errors.
	the ~~flag~~ can have a significant impact on the compute time for
	QP calculations. For large systems, the FFT's usually do not
	~~dominating~~ the computational ~~work load~~ and savings are expected to be small for {{TAG\|PRECFOCK}} = ''fast''.
	QP shifts are usually not very sensitive to the setting of {{TAG\|PRECFOCK}}
	(and it therefore ~~does not~~ harm ~~to set~~ {{TAG\|PRECFOCK}} = ''fast''), whereas for
	RPA calculations we recommend to set {{TAG\|PRECFOCK}} = ''normal'' to avoid numerical errors.

	== Related Tags and Sections ==		== Related Tags and Sections ==
Line 73:		Line 48:

	== Further reading ==		== Further reading ==
	*~~A comprehensive study of the performance of the convergence of GW calculations can be found <ref name="klimes:prb:14"/>.~~ Generally QP energies converge like one over the number of orbitals and one over the number of plane waves in the response function. For basis set converged calculations we recommend ~~to use~~ the strategies in Ref. ~~<ref name="~~klimes:prb:14~~"/>~~		*Generally, QP energies converge like one over the number of orbitals and one over the number of plane waves in the response function. For basis set converged calculations, we recommend using the strategies outlined in Ref. {{cite\|klimes:prb:14}}, which contains a comprehensive study of the performance of the convergence of GW calculations.

	== References ==		== References ==
	~~<references>~~
	~~<ref name="harl:08"> [https://doi.org/10.1103/PhysRevB.77.045136~~
	~~J. Harl, and G. Kresse, "Cohesive energy curves for noble gas solids calculated by adiabatic connection fluctuation-dissipation theory.", Phys. Rev. B 77.4 045136 (2008).]</ref>~~

	~~<ref name="klimes:prb:14"> [http://dx.doi.org/10.1103/PhysRevB.90.075125 J. Klimes, M. Kaltak, and G. Kresse, Phys. Rev. B 90, 075125 (2014)]</ref>~~

	~~</references>~~

	----		----

Karsai at 09:02, 18 March 2019

2019-03-18T09:02:36Z

← Older revision		Revision as of 09:02, 18 March 2019
Line 23:		Line 23:
	reasonable results at fairly modest computational cost, although, the response function		reasonable results at fairly modest computational cost, although, the response function
	contains contributions up to twice the plane wave cutoff <math>G_{\rm cut}</math>		contains contributions up to twice the plane wave cutoff <math>G_{\rm cut}</math>
	(see ~~Sec.~~ {{TAG\|ALGO~~-WRAP~~}}).		(see {{TAG\|ALGO}}).
	Furthermore, RPA correlation energies are reported using an internal extrapolation of the correlation		Furthermore, RPA correlation energies are reported using an internal extrapolation of the correlation
	energy by varying {{TAG\|ENCUTGW}} internally (inside VASP) between the largest value given in the INCAR		energy by varying {{TAG\|ENCUTGW}} internally (inside VASP) between the largest value given in the INCAR

Karsai: /* References */

2019-03-11T14:56:43Z

References

← Older revision		Revision as of 14:56, 11 March 2019
Line 87:		Line 87:
	[[The_VASP_Manual\|Contents]]		[[The_VASP_Manual\|Contents]]

	[[Category:INCAR]][[Category:GW]]		[[Category:INCAR]][[Category:Many-Body Perturbation Theory]][[Category:GW]]

Karsai at 11:13, 20 November 2018

2018-11-20T11:13:26Z

← Older revision		Revision as of 11:13, 20 November 2018
Line 1:		Line 1:
	{{TAGDEF\|ENCUTGW\|[real] ~~energy cutoff for response function~~\| 2/3 {{TAG\|ENCUT}}}}		{{TAGDEF\|ENCUTGW\|[real]\| 2/3 {{TAG\|ENCUT}}}}


	Description: The ~~parameter~~ {{TAG\|ENCUTGW}} controls the basis set for the response functions		Description: The tag {{TAG\|ENCUTGW}} sets the energy cutoff for response function. It controls the basis set for the response functions
	in exactly the same manner as {{TAG\|ENCUT}} does for the orbitals.		in exactly the same manner as {{TAG\|ENCUT}} does for the orbitals.

Kresse at 16:09, 15 September 2017

2017-09-15T16:09:15Z

← Older revision		Revision as of 16:09, 15 September 2017
Line 47:		Line 47:
	* use the default for ENCUTGW, or even decrease ENCUTGW to half the value of ENCUT.		* use the default for ENCUTGW, or even decrease ENCUTGW to half the value of ENCUT.
	* Calculate all orbitals that the plane wave basis set allows to calculate. This number can be determined by searching for "maximum number of plane-waves" in the groundstate DFT OUTCAR file, and setting {{TAG\|NBANDS}} to this value.		* Calculate all orbitals that the plane wave basis set allows to calculate. This number can be determined by searching for "maximum number of plane-waves" in the groundstate DFT OUTCAR file, and setting {{TAG\|NBANDS}} to this value.
	* Increase ENCUT systematically and plot the QP energies versus the number of plane wave coefficients (which equals the number of orbitals). This means ENCUTGW ~~increases~~ as ENCUT increases.		* Increase ENCUT systematically and plot the QP energies versus the number of plane wave coefficients (which equals the number of orbitals). This means ENCUTGW and NBANDS increase as ENCUT increases.

	This procedure can be carried out using few k-points. Other commonly applied methods can yield less accurate results and are not considered		This procedure can be carried out using few k-points. Other commonly applied methods can yield less accurate results and are not considered

Kresse at 16:08, 15 September 2017

2017-09-15T16:08:15Z

← Older revision		Revision as of 16:08, 15 September 2017
Line 46:		Line 46:

	* use the default for ENCUTGW, or even decrease ENCUTGW to half the value of ENCUT.		* use the default for ENCUTGW, or even decrease ENCUTGW to half the value of ENCUT.
	* Calculate all orbitals that the plane wave basis set allows to calculate. This can be determined		* Calculate all orbitals that the plane wave basis set allows to calculate. This number can be determined by searching for "maximum number of plane-waves" in the groundstate DFT OUTCAR file, and setting {{TAG\|NBANDS}} to this value.
	by searching for "maximum number of plane-waves" in the groundstate DFT ~~calculations~~, and setting {{TAG\|NBANDS}} to this value.
	* Increase ENCUT systematically and plot the QP energies versus the number of plane wave coefficients (which equals the number of orbitals). This means ENCUTGW increases as ENCUT increases.		* Increase ENCUT systematically and plot the QP energies versus the number of plane wave coefficients (which equals the number of orbitals). This means ENCUTGW increases as ENCUT increases.

← Older revision		Revision as of 13:48, 6 March 2023
Line 43:		Line 43:
	{{TAG\|ENCUTGWSOFT}},		{{TAG\|ENCUTGWSOFT}},
	{{TAG\|GW calculations}},		{{TAG\|GW calculations}},
	~~{{TAG\|~~ACFDT/~~RPA calculations}}~~		[[ACFDT/RPA_calculations#Basis_set_convergence\|Basis set convergence]]

	{{sc\|ENCUTGW\|Examples\|Examples that use this tag}}		{{sc\|ENCUTGW\|Examples\|Examples that use this tag}}

← Older revision		Revision as of 11:13, 20 November 2018
Line 1:		Line 1:
	{{TAGDEF\|ENCUTGW\|[real] ~~energy cutoff for response function~~\| 2/3 {{TAG\|ENCUT}}}}		{{TAGDEF\|ENCUTGW\|[real]\| 2/3 {{TAG\|ENCUT}}}}


	Description: The ~~parameter~~ {{TAG\|ENCUTGW}} controls the basis set for the response functions		Description: The tag {{TAG\|ENCUTGW}} sets the energy cutoff for response function. It controls the basis set for the response functions
	in exactly the same manner as {{TAG\|ENCUT}} does for the orbitals.		in exactly the same manner as {{TAG\|ENCUT}} does for the orbitals.