# Constrained polarization calculations (Na Sai formalism)

### This page gives hints on how to optimize the geometry under constrained polarization with the ABINIT package.

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

Mentioned in help_features#6.

### Table of content:

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

### 1. Introduction.

Compute polarization in cartesian coordinates, and update lattice constants and atomic positions in order to perform a structural optimization at constrained polarization, following the formalism described in Na Sai et al, PRB 66, 104108 (2002). More details in polflag. The geometry optimization is done in ANADDB.
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### 2. Related input variables.

Compulsory input variables:

... polflag@anaddb [POLarization FLAG]

Useful input variables:

... iatfix@anaddb [Indices of the AToms that are FIXed]
... istrfix@anaddb [Index of STRain FIXed]
... natfix@anaddb [Number of AToms FIXed]
... nstrfix@anaddb [Number of STRain components FIXed]
... relaxat@anaddb [RELAXation of AToms]
... relaxstr@anaddb [RELAXation of STRain]
... targetpol@anaddb [TARGET POLarization]
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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/v4/Input: t71.in t74.in t77.in
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