# Geometry optimization

### This page gives hints on how to perform a geometry optimization with the ABINIT package.

##### Copyright (C) 2016-2017 ABINIT group (GG)

Mentioned in topic_GeoConstraints, help_features#4.

### Table of content:

- 1. Introduction.
- 2. Related input variables.
- 3. Selected input files.

### 1. Introduction.

Different algorithms (Broyden; modified Broyden; Verlet with sudden stop of atoms) allows to find the equilibrium configuration of the nuclei, for which the forces vanish, see ionmov. The cell parameters can also be optimized concurently with the atomic positions optcell, possibly with a state of given stress as a target, strtarget.

Specified lattice parameters, or angles, or atomic positions, can be kept fixed if needed, see topic_GeoConstraints.

A genetic algorithm has been coded, for global optimisation. Not in production yet. See ga_rules.
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### 2. Related input variables.

Compulsory input variables:

... ionmov [IONic MOVEs]
... optcell [OPTimize the CELL shape and dimensions]

Basic input variables:

... dilatmx [lattice DILATation : MaXimal value]
... ntime [Number of TIME steps]
... strfact [STRess FACTor]
... tolmxde [TOLerance on the MaXimal Difference in Energy]
... tolmxf [TOLerance on the MaXimal Force]

Useful input variables:

... iprcfc [Integer for PReConditioner of Force Constants]
... restartxf [RESTART from (X,F) history]
... strprecon [STRess PRECONditioner]
... strtarget [STRess TARGET]

Input variables for experts:

... chkdilatmx [CHecK DILATMX]
... fxcartfactor [Forces to (X) CARTesian coordinates FACTOR]
... ga_algor [Genetic Algorithm - ALGOrithm selection]
... ga_fitness [Genetic Algorithm FITNESS function selection]
... ga_n_rules [Genetic Algorithm Number of RULES]
... ga_opt_percent [Genetic Algorithm OPTimal PERCENT]
... ga_rules [Genetic Algorithm RULES]
... goprecon [Geometry Optimization PRECONditioner equations]
... goprecprm [Geometry Optimization PREconditioner PaRaMeters equations]
... random_atpos [RANDOM ATomic POSitions]
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### 3. Selected input files.

WARNING : as of ABINITv8.6.x, the list of input files provided in the specific section of the topics Web pages is still to be reviewed/tuned. In some cases, it will be adequate, and in other cases, it might be incomplete, or perhaps even useless.
The user can find some related example input files in the ABINIT package in the directory /tests, or on the Web:

tests/v1/Input: t44.in t78.in t79.in t80.in t81.in t82.in

tests/v2/Input: t44.in t48.in t88.in

tests/v3/Input: t40.in t42.in

tests/v5/Input: t02.in t77.in t79.in

tests/v6/Input: t27.in

tests/v7/Input: t10.in
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