# How to estimate anisotropic isothermal compressibility in GROMACS **URL:** \ **Category:** User discussions\ **Created:** [September 8, 2020, 11:06am UTC](https://gromacs.bioexcel.eu/t/how-to-estimate-anisotropic-isothermal-compressibility-in-gromacs/785 "2020-09-08T11:06:12Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![ftorazyne](https://avatars.discourse-cdn.com/v4/letter/f/46a35a/32.png) [@ftorazyne](https://gromacs.bioexcel.eu/u/ftorazyne)\ **Post date:** [September 8, 2020, 11:06am UTC](https://gromacs.bioexcel.eu/t/how-to-estimate-anisotropic-isothermal-compressibility-in-gromacs/785/1 "2020-09-08T11:06:13Z")
GROMACS version: 2019.4 GROMACS modification: No Dear GROMACS users and developers, I have a question about methods of estimation of _anisotropic_ isothermal compressibility by means of GROMACS. I know that gmx energy can estimate isothermal compressibility analysing fluctuations of volume during NPT simulation ([M. P. Allen and D. J. Tildesley, Computer simulation of liquids, Oxford university press, 1989](https://datagrid.hu/boda/Boda-sajat/Rush/Books/Allen-Tildesley.pdf)). But it is an isothermal compressibility for isotropic pressure coupling. On the second thought, I found an alternative [approach](https://www.jics.utk.edu/files/images/recsem-reu/2018/md/Report.pdf), estimating isothermal compressibility by linear approximation of dependency of volume logarithm on pressure. I tried this method, and obtained isothermal compressibility coinciding with «compressibility» value which was preset in \*.mdp file. Is it correct method? Potentially, it may give _anisotropic_ isothermal compressibility, if one used anisotropic pressure coupling varying one pressure component with constant other ones. I need estimation of isothermal compressibilities for simulation of smectic liquid crystals: such system is to have anisotropic compressibility. Is there any correct way to estimate this value?