NELMDL - Revision history

Ftran at 13:44, 27 November 2023

2023-11-27T13:44:26Z

← Older revision		Revision as of 13:44, 27 November 2023
Line 1:		Line 1:
	{{TAGDEF\|NELMDL\|[integer]}}		{{TAGDEF\|NELMDL\|[integer]}}
	{{DEF\|NELMDL\|-12\|if {{TAG\|ISTART}}{{=}}0, {{TAG\|INIWAV}}{{=}}1, and {{TAG\|IALGO}}{{=}}48 or {{TAG\|IALGO}}{{=}}50\|-5\| else}}		{{DEF\|NELMDL\|-12\|if {{TAG\|ISTART}}{{=}}0, {{TAG\|INIWAV}}{{=}}1, and {{TAG\|IALGO}}{{=}}48 or {{TAG\|IALGO}}{{=}}50\|0\|if {{TAG\|WAVECAR}} is present\|-5\| else}}

	Description: {{TAG\|NELMDL}} specifies the number of non-self-consistent steps at the beginning.		Description: {{TAG\|NELMDL}} specifies the number of non-self-consistent steps at the beginning.

Ftran at 10:32, 27 November 2023

2023-11-27T10:32:15Z

← Older revision		Revision as of 10:32, 27 November 2023
Line 6:		Line 6:
	If the orbitals are initialized using a random number generator (the default in VASP), the initial orbitals are usually unreasonable and the iterative matrix diagonalization will require 5-10 steps to obtain reasonable orbitals. The charge density corresponding to the initial orbitals is also, at best, erratic. It is hence advisable to perform a few electronic steps while keeping the initial Hamiltonian fixed. This initial Hamiltonian is usually determined from a superposition of atomic charge densities (see {{TAG\|ICHARG}}).		If the orbitals are initialized using a random number generator (the default in VASP), the initial orbitals are usually unreasonable and the iterative matrix diagonalization will require 5-10 steps to obtain reasonable orbitals. The charge density corresponding to the initial orbitals is also, at best, erratic. It is hence advisable to perform a few electronic steps while keeping the initial Hamiltonian fixed. This initial Hamiltonian is usually determined from a superposition of atomic charge densities (see {{TAG\|ICHARG}}).

	Such a 'delay' is absolutely necessary. if the SCF-convergence is slow and problematic (e.g. for surfaces or metallic clusters, low dimensional system). Without a delay, VASP will most likely not converge, or at least the convergence speed is slowed significantly.		Such a 'delay' is absolutely necessary if the SCF-convergence is slow and problematic (e.g. for surfaces or metallic clusters, low dimensional system). Without a delay, VASP will most likely not converge, or at least the convergence speed is slowed significantly.

	{{TAG\|NELMDL}} might be set to a positive or negative value. A negative value means that the delay is only performed in the first ionic step (usually the recommended option). A positive number means that a delay is employed after each ionic movement. This can improve the convergence speed in VASP.6 (see below) but is not recommended in VASP.5.		{{TAG\|NELMDL}} might be set to a positive or negative value. A negative value means that the delay is only performed in the first ionic step (usually the recommended option). A positive number means that a delay is employed after each ionic movement. This can improve the convergence speed in VASP.6 (see below) but is not recommended in VASP.5.

Karsai: /* Related tags and articles */

2022-04-07T15:35:43Z

Karsai: /* Related Tags and Sections */

2022-04-07T15:35:35Z

Related Tags and Sections

← Older revision		Revision as of 15:35, 7 April 2022
Line 18:		Line 18:
	* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal to 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3 can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.		* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal to 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3 can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.

	== Related ~~Tags~~ and ~~Sections~~ ==		== Related tags and articles ==
	{{TAG\|NELM}},		{{TAG\|NELM}},
	{{TAG\|NELMIN}}		{{TAG\|NELMIN}},
	{{TAG\|IALGO}}		{{TAG\|IALGO}}

Karsai at 11:17, 7 April 2022

2022-04-07T11:17:31Z

← Older revision		Revision as of 11:17, 7 April 2022
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	Special considerations for VASP.6:		Special considerations for VASP.6:

	* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step) does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.		* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step) does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.

	* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal to 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3 can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.		* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal to 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3 can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.

Karsai at 11:16, 7 April 2022

2022-04-07T11:16:33Z

← Older revision		Revision as of 11:16, 7 April 2022
Line 16:		Line 16:
	* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step) does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.		* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step) does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.

	* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3, can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.		* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal to 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3 can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.

	== Related Tags and Sections ==		== Related Tags and Sections ==

Karsai at 11:15, 7 April 2022

2022-04-07T11:15:42Z

← Older revision		Revision as of 11:15, 7 April 2022
Line 14:		Line 14:
	Special considerations for VASP.6:		Special considerations for VASP.6:

	* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step) does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file, since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.		* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step) does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.

	* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3, can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.		* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3, can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.

Huebsch at 14:35, 6 April 2022

2022-04-06T14:35:09Z

Karsai at 14:02, 6 April 2022

2022-04-06T14:02:10Z

← Older revision		Revision as of 14:02, 6 April 2022
Line 16:		Line 16:
	* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step), does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file, since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.		* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step), does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file, since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.

	* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient, if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3, can thus improve the stability and performance during relaxations using HF type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3, if you encounter convergence issues during relaxations using HF-type Hamiltonians.		* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient, if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3, can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3, if you encounter convergence issues during relaxations using HF-type Hamiltonians.

	== Related Tags and Sections ==		== Related Tags and Sections ==

Karsai at 14:01, 6 April 2022

2022-04-06T14:01:45Z

← Older revision		Revision as of 14:01, 6 April 2022
Line 16:		Line 16:
	* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step), does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file, since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.		* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step), does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file, since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.

	* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient, if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3, can thus improve the stability and performance during relaxations using HF type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3, if you encounter convergence issues during relaxations using HF type Hamiltonians.		* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient, if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3, can thus improve the stability and performance during relaxations using HF type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3, if you encounter convergence issues during relaxations using HF-type Hamiltonians.

	== Related Tags and Sections ==		== Related Tags and Sections ==

← Older revision		Revision as of 13:44, 27 November 2023
Line 1:		Line 1:
	{{TAGDEF\|NELMDL\|[integer]}}		{{TAGDEF\|NELMDL\|[integer]}}
	{{DEF\|NELMDL\|-12\|if {{TAG\|ISTART}}{{=}}0, {{TAG\|INIWAV}}{{=}}1, and {{TAG\|IALGO}}{{=}}48 or {{TAG\|IALGO}}{{=}}50\|-5\| else}}		{{DEF\|NELMDL\|-12\|if {{TAG\|ISTART}}{{=}}0, {{TAG\|INIWAV}}{{=}}1, and {{TAG\|IALGO}}{{=}}48 or {{TAG\|IALGO}}{{=}}50\|0\|if {{TAG\|WAVECAR}} is present\|-5\| else}}

	Description: {{TAG\|NELMDL}} specifies the number of non-self-consistent steps at the beginning.		Description: {{TAG\|NELMDL}} specifies the number of non-self-consistent steps at the beginning.

← Older revision		Revision as of 15:35, 7 April 2022
Line 18:		Line 18:
	* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal to 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3 can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.		* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal to 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3 can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.

	== Related ~~Tags~~ and ~~Sections~~ ==		== Related tags and articles ==
	{{TAG\|NELM}},		{{TAG\|NELM}},
	{{TAG\|NELMIN}}		{{TAG\|NELMIN}},
	{{TAG\|IALGO}}		{{TAG\|IALGO}}

← Older revision		Revision as of 15:35, 7 April 2022
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	----		----

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

← Older revision		Revision as of 14:35, 6 April 2022
Line 2:		Line 2:
	{{DEF\|NELMDL\|-12\|if {{TAG\|ISTART}}{{=}}0, {{TAG\|INIWAV}}{{=}}1, and {{TAG\|IALGO}}{{=}}48 or {{TAG\|IALGO}}{{=}}50\|-5\| else}}		{{DEF\|NELMDL\|-12\|if {{TAG\|ISTART}}{{=}}0, {{TAG\|INIWAV}}{{=}}1, and {{TAG\|IALGO}}{{=}}48 or {{TAG\|IALGO}}{{=}}50\|-5\| else}}

	Description: {{TAG\|NELMDL}} specifies the number of non-~~selfconsistent~~ steps at the beginning.		Description: {{TAG\|NELMDL}} specifies the number of non-self-consistent steps at the beginning.
	----		----
	If the orbitals are initialized using a random number generator (the default in VASP), the initial orbitals are usually unreasonable and the iterative matrix diagonalization will ~~required~~ 5-10 steps to obtain reasonable orbitals. The charge density corresponding to the initial orbitals is also, at best, erratic. It is hence advisable to perform a few electronic steps while keeping the initial Hamiltonian fixed. This initial Hamiltonian is usually determined from a superposition of atomic charge densities (see {{TAG\|ICHARG}}).		If the orbitals are initialized using a random number generator (the default in VASP), the initial orbitals are usually unreasonable and the iterative matrix diagonalization will require 5-10 steps to obtain reasonable orbitals. The charge density corresponding to the initial orbitals is also, at best, erratic. It is hence advisable to perform a few electronic steps while keeping the initial Hamiltonian fixed. This initial Hamiltonian is usually determined from a superposition of atomic charge densities (see {{TAG\|ICHARG}}).

	Such a 'delay' is absolutely necessary. if the SCF-convergence is slow and problematic (e.g. for surfaces or metallic clusters, low dimensional system). Without a delay, VASP will most likely not converge or at least the convergence speed is slowed significantly.		Such a 'delay' is absolutely necessary. if the SCF-convergence is slow and problematic (e.g. for surfaces or metallic clusters, low dimensional system). Without a delay, VASP will most likely not converge, or at least the convergence speed is slowed significantly.

	{{TAG\|NELMDL}} might be set to a positive or negative value. A negative value means that the delay is only performed in the first ionic step (usually the recommended option). A positive number means that a delay is employed after each ionic movement. This can improve the convergence speed in VASP.6 (see below), but is not recommended in VASP.5.		{{TAG\|NELMDL}} might be set to a positive or negative value. A negative value means that the delay is only performed in the first ionic step (usually the recommended option). A positive number means that a delay is employed after each ionic movement. This can improve the convergence speed in VASP.6 (see below) but is not recommended in VASP.5.

	For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED), the Davidson algorithm is used during the delay phase and the Hamiltonian is kept fixed during these steps.		For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED), the Davidson algorithm is used during the delay phase and the Hamiltonian is kept fixed during these steps.
Line 14:		Line 14:
	Special considerations for VASP.6:		Special considerations for VASP.6:

	* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step), does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file, since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.		* For calculations using a direct minimization of the Hamiltonian ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED): if {{TAG\|NELMDL}} is set, the Davidson algorithm is used in the first {{TAG\|NELMDL}} steps as described above. Using a positive {{TAG\|NELMDL}} (i.e. delay in every ionic step) does not work reliably in VASP.5, due to issues in the orbital and charge density prediction. In VASP.6, using {{TAG\|NELMDL}}=1 (or {{TAG\|NELMDL}}=2) and direct minimization, often improves the stability and efficiency of molecular dynamics simulations or relaxations ({{TAG\|ALGO}}=ALL or {{TAG\|ALGO}}=DAMPED). Note, however, that this might require one to prepare a reasonable {{TAG\|WAVECAR}} file, since {{TAG\|NELMDL}} =1/2 might not suffice to obtain a reasonable set of orbitals from the initial random numbers.

	* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient, if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3, can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3, if you encounter convergence issues during relaxations using HF-type Hamiltonians.		* For HF-type calculations, if {{TAG\|NELMDL}} is larger or equal 3, VASP will perform {{TAG\|NELMDL}} non-selfconsistent steps using the Davidson algorithm, and a local Hamiltonian is calculated using the semi-local DFT functional corresponding to the chosen hybrid functional (i.e. PBE for HSE and PBE0). This is expedient if the ions move by a large distance between the ionic steps. Setting {{TAG\|NELMDL}} =3, can thus improve the stability and performance during relaxations using HF-type Hamiltonians. Try to use {{TAG\|ALGO}}=All and {{TAG\|NELMDL}}=3 if you encounter convergence issues during relaxations using HF-type Hamiltonians.

	== Related Tags and Sections ==		== Related Tags and Sections ==
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	----		----

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