Structure optimization - Revision history

Wolloch: /* Common considerations */

2025-04-17T12:06:37Z

Common considerations

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	The quantity <tt>trialstep</tt> is the size of the current trialstep.		The quantity <tt>trialstep</tt> is the size of the current trialstep.
	Multiply the current value of {{TAG\|POTIM}} with this number to obtain the optimal step size.		Multiply the current value of {{TAG\|POTIM}} with this number to obtain the optimal step size.
			{{NB\|mind\|If you use the default value of {{TAGO\|ISYM\|2}}, lower symmetry structures will be inaccessible to the relaxation algorithms. It is usually preferable to break symmetries intentionally by modifying the starting structure instead of turning symmetry operations off via {{TAGO\|ISYM\|0}}.}}

	== RMM-DIIS ==		== RMM-DIIS ==

2024-10-21T11:39:28Z

RMM-DIIS

← Older revision		Revision as of 11:39, 21 October 2024
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	For {{TAGO\|IBRION\|1}}, VASP uses a RMM-DIIS algorithm to relax the ions into their instantaneous groundstate.		For {{TAGO\|IBRION\|1}}, VASP uses a RMM-DIIS algorithm to relax the ions into their instantaneous groundstate.
	RMM-DIIS stands for ''residual-minimization method, direct inversion of the iterative subspace''.{{cite\|pulay:cpl:1980}}		RMM-DIIS stands for ''residual-minimization method, direct inversion in the iterative subspace''.{{cite\|pulay:cpl:1980}}
	The forces and the stress tensor determine the search directions for finding the equilibrium positions; the total energy is not taken into account.		The forces and the stress tensor determine the search directions for finding the equilibrium positions; the total energy is not taken into account.
	This algorithm is very fast and efficient close to a local minimum, but fails badly if the initial positions are a bad guess (use [[#Conjugate gradient\|conjugate gradient]] instead).		This algorithm is very fast and efficient close to a local minimum, but fails badly if the initial positions are a bad guess (use [[#Conjugate gradient\|conjugate gradient]] instead).

2024-10-18T11:15:38Z

References

← Older revision		Revision as of 11:15, 18 October 2024
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	<references/>		<references/>

	[[Category:Ionic minimization]][[Category:Howto]]		[[Category:Ionic minimization]][[Category:Howto]][[Category:Forces]]

2024-10-18T11:13:39Z

← Older revision		Revision as of 11:13, 18 October 2024
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	In both cases ''g(F)'' and ''g(S)'' are the norm of forces and stress.		In both cases ''g(F)'' and ''g(S)'' are the norm of forces and stress.
	The extra line in the latter case is a sanity check on the average velocities and should produce vanishingly small numbers.		The extra line in the latter case is a sanity check on the average velocities and should produce vanishingly small numbers.

	~~== References ==~~
	~~<references/>~~

	== Related tags and articles ==		== Related tags and articles ==
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	{{TAG\|NSW}},		{{TAG\|NSW}},
	{{TAG\|SMASS}}		{{TAG\|SMASS}}

			== References ==
			<references/>

	[[Category:Ionic minimization]][[Category:Howto]]		[[Category:Ionic minimization]][[Category:Howto]]

2024-10-18T11:13:05Z

References

← Older revision		Revision as of 11:13, 18 October 2024
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	== References ==		== References ==
	<references/>		<references/>

			== Related tags and articles ==
			{{TAG\|IBRION}},
			{{TAG\|POTIM}},
			{{TAG\|NSW}},
			{{TAG\|SMASS}}

	[[Category:Ionic minimization]][[Category:Howto]]		[[Category:Ionic minimization]][[Category:Howto]]

2024-10-18T11:11:59Z

← Older revision		Revision as of 11:11, 18 October 2024
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	== References ==		== References ==
	<references/>		<references/>

			[[Category:Ionic minimization]][[Category:Howto]]

2024-10-18T11:06:01Z

← Older revision	Revision as of 11:06, 18 October 2024
(No difference)

2024-10-18T11:05:47Z

← Older revision	Revision as of 11:05, 18 October 2024
(No difference)

2024-10-18T08:44:57Z

← Older revision		Revision as of 08:44, 18 October 2024
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	Even simpler are [[#Damped molecular dynamics\|damped molcular dynamics]] ({{TAGO\|IBRION\|3}}).		Even simpler are [[#Damped molecular dynamics\|damped molcular dynamics]] ({{TAGO\|IBRION\|3}}).
	This algorithm propagates through time using the forces and friction on the velocities.		This algorithm propagates through time using the forces and friction on the velocities.


	All relaxation algorithms ({{TAG\|IBRION}}=1, 2, and 3) rely on a step size {{TAG\|POTIM}}.		All relaxation algorithms ({{TAG\|IBRION}}=1, 2, and 3) rely on a step size {{TAG\|POTIM}}.

2024-10-18T08:44:32Z

Common considerations

← Older revision		Revision as of 08:44, 18 October 2024
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	Next, you need to decide on an algorithm by setting the {{TAG\|IBRION}} tag.		Next, you need to decide on an algorithm by setting the {{TAG\|IBRION}} tag.
	In ~~the figure~~ 1, we show some heuristic rules that may help to decide with this selection.		In Figure 1, we show some heuristic rules that may help to decide with this selection.
	These guidelines are a compromise between speed and robustness of the algorithms.		These guidelines are a compromise between speed and robustness of the algorithms.
	The [[#RMM-DIIS\|RMM-DIIS algorithm]] ({{TAGO\|IBRION\|1}}) is very efficient because it uses the history of many steps to obtain the best next guess.		The [[#RMM-DIIS\|RMM-DIIS algorithm]] ({{TAGO\|IBRION\|1}}) is very efficient because it uses the history of many steps to obtain the best next guess.