Troubleshooting electronic convergence - Revision history

Huebsch at 12:16, 14 October 2024

2024-10-14T12:16:32Z

← Older revision		Revision as of 12:16, 14 October 2024
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	There can be many reasons why convergence to the electronic ground state fails. Below you find some strategies to overcome convergence issues in the [[:Category:Electronic minimization\|electronic minimization]].		There can be many reasons why convergence to the electronic ground state fails. Below you find some general strategies to overcome convergence issues in the [[:Category:Electronic minimization\|electronic minimization]] and some recommendations for specific cases, e.g., charged systems or magnetic systems.

	== Step-by-step instructions ==		== Step-by-step instructions ==

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	# First, converge the calculation with {{TAG\|LDIPOL}}=.FALSE. Store the {{FILE\|WAVECAR}} in the same folder.		# First, converge the calculation with {{TAG\|LDIPOL}}=.FALSE. Store the {{FILE\|WAVECAR}} in the same folder.
	# Use the {{FILE\|WAVECAR}} to restart the calculation with {{TAG\|LDIPOL}}=.TRUE.		# Use the {{FILE\|WAVECAR}} to restart the calculation with {{TAG\|LDIPOL}}=.TRUE.

			=== Magnetic calculations ===

			What can one do when convergence is bad:
			*Start from charge density of non-spin-polarized calculation using {{TAG\|ISTART}}=0 (or remove the {{TAG\|WAVECAR}} file) and {{TAG\|ICHARG}}=1.
			*Use linear mixing by setting {{TAG\|BMIX}}=0.0001 and {{TAG\|BMIX_MAG}}=0.0001.
			*Mix slowly, i.e., reduce {{TAG\|AMIX}} and {{TAG\|AMIX_MAG}}.
			*REDUCE {{TAG\|MAXMIX}}, the number of steps stored in the Broyden mixer (default {{TAG\|MAXMIX}}=45).
			*Restart from partially converged results (stop a calculation after say 20 steps and restart from the {{TAG\|WAVECAR}} file).
			*Use constraints to stabilize the magnetic configuration.

	[[Category:Howto]][[Category:Electronic minimization]]		[[Category:Howto]][[Category:Electronic minimization]]

Svijay: /* Method-specific recommendations */

2024-06-07T14:55:18Z

Method-specific recommendations

← Older revision		Revision as of 14:55, 7 June 2024
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	Similar to the [[#Magnetic calculation with LDA+U\|recipe for magnetic calculation with LDA+U]], it might be helpful to run steps 1. to 3. with a low {{TAG\|ENCUT}} and then perform step 3. again with the desired {{TAG\|ENCUT}}.		Similar to the [[#Magnetic calculation with LDA+U\|recipe for magnetic calculation with LDA+U]], it might be helpful to run steps 1. to 3. with a low {{TAG\|ENCUT}} and then perform step 3. again with the desired {{TAG\|ENCUT}}.

			=== Dipole Correction ===
			# First, converge the calculation with {{TAG\|LDIPOL}}=.FALSE. Store the {{FILE\|WAVECAR}} in the same folder.
			# Use the {{FILE\|WAVECAR}} to restart the calculation with {{TAG\|LDIPOL}}=.TRUE.

	[[Category:Howto]][[Category:Electronic minimization]]		[[Category:Howto]][[Category:Electronic minimization]]

Miranda.henrique: /* Step-by-step instructions */

2023-11-15T06:22:49Z

Step-by-step instructions

← Older revision		Revision as of 06:22, 15 November 2023
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	'''Step 1:''' Simplify the calculation and reduce time-to-solution. Try to create a minimal [[INCAR]] file with as few tags as possible. If the calculation converges, then gradually add them back until you find which one was causing the problem. Try to reduce the time-to-solution as much as possible by lowering the '''k'''-point sampling (or using gamma-only calculations if applicable), lower {{TAG\|ENCUT}}, use {{TAG\|PREC}}=Normal.		'''Step 1:''' Simplify the calculation and reduce time-to-solution. Try to create a minimal [[INCAR]] file with as few tags as possible. If the calculation converges, then gradually add them back until you find which one was causing the problem. Try to reduce the time-to-solution as much as possible by lowering the '''k'''-point sampling (or using gamma-only calculations if applicable), lower {{TAG\|ENCUT}}, use {{TAG\|PREC}}=Normal.

	'''Step 2:''' ~~Fixing~~ the ~~charge density (for cases where density mixing is used)~~		'''Step 2:''' Check the value of {{TAG\|ISMEAR}}. If you have partially occupied states set {{TAG\|ISMEAR}}=-1 or 1.

	'''Step 3:''' ~~Increase {{TAG\|NBANDS}}. Check if you have enough bands. You can do this by looking at~~ the [[OUTCAR]] file and checking that there are enough empty states, i.e., states with zero occupation. When using an iterative solver, the last states might not be accurately described, if these are occupied, then convergence is likely to fail. Often, the VASP default setting for ~~{{TAG\|NBANDS}}~~ is ~~insufficient for systems with f-orbitals or calculations with meta-GGA's.~~		'''Step 3:''' Fixing the charge density (for cases where density mixing is used)

	'''Step 4:''' ~~Switch~~ {{TAG\|~~ALGO~~}}.		'''Step 4:''' Increase {{TAG\|NBANDS}}. Check if you have enough bands. You can do this by looking at the [[OUTCAR]] file and checking that there are enough empty states, i.e., states with zero occupation. When using an iterative solver, the last states might not be accurately described, if these are occupied, then convergence is likely to fail. Often, the VASP default setting for {{TAG\|NBANDS}} is insufficient for systems with f-orbitals or calculations with meta-GGA's.

	'''Step 5:''' For {{TAG\|IALGO}}=5X or 4X change {{TAG\|TIME}}.		'''Step 5:''' Switch {{TAG\|ALGO}}.

			'''Step 6:''' For {{TAG\|IALGO}}=5X or 4X change {{TAG\|TIME}}.

	== Method-specific recommendations ==		== Method-specific recommendations ==

Huebsch at 13:57, 20 October 2023

2023-10-20T13:57:29Z

← Older revision		Revision as of 13:57, 20 October 2023
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	There can be many reasons why convergence to the electronic ground state fails. Below you find some strategies to overcome convergence issues in the [[Category:Electronic minimization\|electronic minimization]].		There can be many reasons why convergence to the electronic ground state fails. Below you find some strategies to overcome convergence issues in the [[:Category:Electronic minimization\|electronic minimization]].
	== Step-by-step instructions ==		== Step-by-step instructions ==

Huebsch: /* Step-by-step instructions */

2023-10-20T13:56:18Z

Step-by-step instructions

← Older revision		Revision as of 13:56, 20 October 2023
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	'''Step 4:''' Switch {{TAG\|ALGO}}.		'''Step 4:''' Switch {{TAG\|ALGO}}.

	'''Step 5:''' For {{TAG\|~~ALGO~~}}=5X or 4X change {{TAG\|TIME}}.		'''Step 5:''' For {{TAG\|IALGO}}=5X or 4X change {{TAG\|TIME}}.

	== Method-specific recommendations ==		== Method-specific recommendations ==

Huebsch at 10:52, 20 October 2023

2023-10-20T10:52:49Z

← Older revision		Revision as of 10:52, 20 October 2023
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	There can be many reasons why the ~~SCF~~ convergence ~~is not reached~~.		There can be many reasons why convergence to the electronic ground state fails. Below you find some strategies to overcome convergence issues in the [[Category:Electronic minimization\|electronic minimization]].
	~~Naturally, there are also many different possible solutions.~~		== Step-by-step instructions ==

	Try to create a minimal [[INCAR]] file with as few tags as possible.		'''Step 1:''' Simplify the calculation and reduce time-to-solution. Try to create a minimal [[INCAR]] file with as few tags as possible. If the calculation converges, then gradually add them back until you find which one was causing the problem. Try to reduce the time-to-solution as much as possible by lowering the '''k'''-point sampling (or using gamma-only calculations if applicable), lower {{TAG\|ENCUT}}, use {{TAG\|PREC}}=Normal.
	If the calculation converges then gradually add them back until you find which one was causing the problem.
	Try to reduce the time-to-solution as much as possible by lowering the '''k''' point sampling (or using gamma-only calculations ~~is that is sensible~~), lower {{TAG\|ENCUT}}, use {{TAG\|PREC}}=Normal.

	~~Check if you have enough bands. You can do this by looking at the [[OUTCAR]] file and checking that there are enough~~ '~~empty~~' ~~states~~ (~~i.e. states with zero occupation). When using an iterative solver the last states might not be accurately described, if these are occupied then convergence is likely to fail.~~		'''Step 2:''' Fixing the charge density (for cases where density mixing is used)
	~~Often the VASP default setting~~ for ~~{{TAG\|NBANDS}}~~ is ~~insufficient for systems with f-orbitals.~~

	~~Systems~~ with f-orbitals ~~are in general difficult to converge~~.		'''Step 3:''' Increase {{TAG\|NBANDS}}. Check if you have enough bands. You can do this by looking at the [[OUTCAR]] file and checking that there are enough empty states, i.e., states with zero occupation. When using an iterative solver, the last states might not be accurately described, if these are occupied, then convergence is likely to fail. Often, the VASP default setting for {{TAG\|NBANDS}} is insufficient for systems with f-orbitals or calculations with meta-GGA's.

			'''Step 4:''' Switch {{TAG\|ALGO}}.

			'''Step 5:''' For {{TAG\|ALGO}}=5X or 4X change {{TAG\|TIME}}.

			== Method-specific recommendations ==

	In the following, we will describe a few recipes that work for particular systems.		In the following, we will describe a few recipes that work for particular systems.
	Some of these recipes might be transferable ~~but it is hard~~ to ~~provide a recipe that is guaranteed to work for all cases~~.		Some of these recipes might be transferable even to other methods.
			=== Magnetic calculation with LDA+U ===
	== Magnetic calculation with LDA+U ==		Magnetic calculations present a lot of challenges, in particular when the energy differences between different magnetic configurations are small.
	Magnetic calculations present a lot of challenges in particular when the energy differences between different magnetic configurations are ~~not large~~.
	Our recommendation is to split the calculation into multiple steps:		Our recommendation is to split the calculation into multiple steps:
	# give initial magnetization only to the magnetic atoms		# give initial magnetization only to the magnetic atoms
Line 24:		Line 26:
	## step 3 add LDA+U tags keeping {{TAG\|ALGO}}=All and small {{TAG\|TIME}}		## step 3 add LDA+U tags keeping {{TAG\|ALGO}}=All and small {{TAG\|TIME}}

	It might be ~~useful~~ to split step 1. in two by first running with a smaller {{TAG\|ENCUT}} and then restarting the calculation from the {{FILE\|WAVECAR}} with the desired {{TAG\|ENCUT}}		It might be helpful to split step 1. in two by first running with a smaller {{TAG\|ENCUT}} and then restarting the calculation from the {{FILE\|WAVECAR}} with the desired {{TAG\|ENCUT}}.

	~~== MBJ calculation ==~~

			=== MBJ calculation ===
	This exchange-correlation functional is not particularly easy to converge in some systems.		This exchange-correlation functional is not particularly easy to converge in some systems.
	For these systems we recommend that you split the calculation into multiple steps that successively bring you closer to the solution (always restarting from the WAVECAR of the previous step):		For these systems, we recommend that you split the calculation into multiple steps that successively bring you closer to the solution (always restarting from the WAVECAR of the previous step):
	# Converge with the PBE functional		# Converge with the PBE functional
	# Converge with the {{TAG\|METAGGA}}=MBJ functional with the {{TAG\|CMBJ}} parameter set to some value and {{TAG\|ALGO}}=All and {{TAG\|TIME}}=0.1		# Converge with the {{TAG\|METAGGA}}=MBJ functional with the {{TAG\|CMBJ}} parameter set to some value and {{TAG\|ALGO}}=All and {{TAG\|TIME}}=0.1
	# Converge with the {{TAG\|METAGGA}}=MBJ functional without {{TAG\|CMBJ}} parameter set and {{TAG\|ALGO}}=All and {{TAG\|TIME}}=0.1		# Converge with the {{TAG\|METAGGA}}=MBJ functional without {{TAG\|CMBJ}} parameter set and {{TAG\|ALGO}}=All and {{TAG\|TIME}}=0.1

	Similar to the [[~~Difficult_to_converge_systems~~#Magnetic calculation with LDA+U\|~~previous~~ recipe]] it might be ~~useful~~ to run steps 1. to 3. with a low {{TAG\|ENCUT}} and then perform step 3. again with the desired {{TAG\|ENCUT}}.		Similar to the [[#Magnetic calculation with LDA+U\|recipe for magnetic calculation with LDA+U]], it might be helpful to run steps 1. to 3. with a low {{TAG\|ENCUT}} and then perform step 3. again with the desired {{TAG\|ENCUT}}.

	[[Category:~~Common Pitfalls~~]]		[[Category:Howto]][[Category:Electronic minimization]]

Huebsch: Huebsch moved page Difficult to converge systems to Troubleshooting electronic convergence

2023-10-20T10:39:55Z

Huebsch moved page Difficult to converge systems to Troubleshooting electronic convergence

← Older revision		Revision as of 10:39, 20 October 2023
(No difference)

Miranda.henrique at 08:27, 20 October 2023

2023-10-20T08:27:26Z

← Older revision		Revision as of 08:27, 20 October 2023
Line 36:		Line 36:
	Similar to the [[Difficult_to_converge_systems#Magnetic calculation with LDA+U\|previous recipe]] it might be useful to run steps 1. to 3. with a low {{TAG\|ENCUT}} and then perform step 3. again with the desired {{TAG\|ENCUT}}.		Similar to the [[Difficult_to_converge_systems#Magnetic calculation with LDA+U\|previous recipe]] it might be useful to run steps 1. to 3. with a low {{TAG\|ENCUT}} and then perform step 3. again with the desired {{TAG\|ENCUT}}.

	~~----~~
	[[Category:Common Pitfalls]]		[[Category:Common Pitfalls]]

Miranda.henrique at 08:45, 27 July 2022

2022-07-27T08:45:09Z

← Older revision		Revision as of 08:45, 27 July 2022
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	Try to create a minimal [[INCAR]] file with as few tags as possible.		Try to create a minimal [[INCAR]] file with as few tags as possible.
	If the calculation converges then gradually add them back until you find which one was causing the problem.		If the calculation converges then gradually add them back until you find which one was causing the problem.
			Try to reduce the time-to-solution as much as possible by lowering the '''k''' point sampling (or using gamma-only calculations is that is sensible), lower {{TAG\|ENCUT}}, use {{TAG\|PREC}}=Normal.

	Check if you have enough bands. You can do this by looking at the [[OUTCAR]] file and checking that there are enough 'empty' states (i.e. states with zero occupation). When using an iterative solver the last states might not be accurately described, if these are occupied ~~them~~ convergence is likely to fail.		Check if you have enough bands. You can do this by looking at the [[OUTCAR]] file and checking that there are enough 'empty' states (i.e. states with zero occupation). When using an iterative solver the last states might not be accurately described, if these are occupied then convergence is likely to fail.
			Often the VASP default setting for {{TAG\|NBANDS}} is insufficient for systems with f-orbitals.

	Systems with f-orbitals are in ~~particular~~ difficult to converge.		Systems with f-orbitals are in general difficult to converge.
	~~Here are a couple of tips for a magnetic calculation with LDA+U:~~

			In the following, we will describe a few recipes that work for particular systems.
			Some of these recipes might be transferable but it is hard to provide a recipe that is guaranteed to work for all cases.

			== Magnetic calculation with LDA+U ==
			Magnetic calculations present a lot of challenges in particular when the energy differences between different magnetic configurations are not large.
			Our recommendation is to split the calculation into multiple steps:
	# give initial magnetization only to the magnetic atoms		# give initial magnetization only to the magnetic atoms
	# use spin-polarized calculation		# use spin-polarized calculation
Line 17:		Line 24:
	## step 3 add LDA+U tags keeping {{TAG\|ALGO}}=All and small {{TAG\|TIME}}		## step 3 add LDA+U tags keeping {{TAG\|ALGO}}=All and small {{TAG\|TIME}}

	It might be useful to split step 1 in two by first running with a smaller {{TAG\|ENCUT}} and then restarting the calculation from the {{FILE\|WAVECAR}} with the desired {{TAG\|ENCUT}}		It might be useful to split step 1. in two by first running with a smaller {{TAG\|ENCUT}} and then restarting the calculation from the {{FILE\|WAVECAR}} with the desired {{TAG\|ENCUT}}

			== MBJ calculation ==

			This exchange-correlation functional is not particularly easy to converge in some systems.
			For these systems we recommend that you split the calculation into multiple steps that successively bring you closer to the solution (always restarting from the WAVECAR of the previous step):
			# Converge with the PBE functional
			# Converge with the {{TAG\|METAGGA}}=MBJ functional with the {{TAG\|CMBJ}} parameter set to some value and {{TAG\|ALGO}}=All and {{TAG\|TIME}}=0.1
			# Converge with the {{TAG\|METAGGA}}=MBJ functional without {{TAG\|CMBJ}} parameter set and {{TAG\|ALGO}}=All and {{TAG\|TIME}}=0.1

			Similar to the [[Difficult_to_converge_systems#Magnetic calculation with LDA+U\|previous recipe]] it might be useful to run steps 1. to 3. with a low {{TAG\|ENCUT}} and then perform step 3. again with the desired {{TAG\|ENCUT}}.

	----		----
	[[Category:Common Pitfalls]]		[[Category:Common Pitfalls]]

Miranda.henrique: Miranda.henrique moved page Diffcult to converge systems to Difficult to converge systems

2022-07-26T09:12:00Z

Miranda.henrique moved page Diffcult to converge systems to Difficult to converge systems

← Older revision	Revision as of 09:12, 26 July 2022
(No difference)

← Older revision		Revision as of 06:22, 15 November 2023
Line 4:		Line 4:
	'''Step 1:''' Simplify the calculation and reduce time-to-solution. Try to create a minimal [[INCAR]] file with as few tags as possible. If the calculation converges, then gradually add them back until you find which one was causing the problem. Try to reduce the time-to-solution as much as possible by lowering the '''k'''-point sampling (or using gamma-only calculations if applicable), lower {{TAG\|ENCUT}}, use {{TAG\|PREC}}=Normal.		'''Step 1:''' Simplify the calculation and reduce time-to-solution. Try to create a minimal [[INCAR]] file with as few tags as possible. If the calculation converges, then gradually add them back until you find which one was causing the problem. Try to reduce the time-to-solution as much as possible by lowering the '''k'''-point sampling (or using gamma-only calculations if applicable), lower {{TAG\|ENCUT}}, use {{TAG\|PREC}}=Normal.

	'''Step 2:''' ~~Fixing~~ the ~~charge density (for cases where density mixing is used)~~		'''Step 2:''' Check the value of {{TAG\|ISMEAR}}. If you have partially occupied states set {{TAG\|ISMEAR}}=-1 or 1.

	'''Step 3:''' ~~Increase {{TAG\|NBANDS}}. Check if you have enough bands. You can do this by looking at~~ the [[OUTCAR]] file and checking that there are enough empty states, i.e., states with zero occupation. When using an iterative solver, the last states might not be accurately described, if these are occupied, then convergence is likely to fail. Often, the VASP default setting for ~~{{TAG\|NBANDS}}~~ is ~~insufficient for systems with f-orbitals or calculations with meta-GGA's.~~		'''Step 3:''' Fixing the charge density (for cases where density mixing is used)

	'''Step 4:''' ~~Switch~~ {{TAG\|~~ALGO~~}}.		'''Step 4:''' Increase {{TAG\|NBANDS}}. Check if you have enough bands. You can do this by looking at the [[OUTCAR]] file and checking that there are enough empty states, i.e., states with zero occupation. When using an iterative solver, the last states might not be accurately described, if these are occupied, then convergence is likely to fail. Often, the VASP default setting for {{TAG\|NBANDS}} is insufficient for systems with f-orbitals or calculations with meta-GGA's.

	'''Step 5:''' For {{TAG\|IALGO}}=5X or 4X change {{TAG\|TIME}}.		'''Step 5:''' Switch {{TAG\|ALGO}}.

			'''Step 6:''' For {{TAG\|IALGO}}=5X or 4X change {{TAG\|TIME}}.

	== Method-specific recommendations ==		== Method-specific recommendations ==