# Constant pH MD

**URL:** <https://gromacs.bioexcel.eu/t/constant-ph-md/7901>\
**Category:** User discussions\
**Tags:** mdp-parameters\
**Created:** [December 21, 2023, 11:26am UTC](https://gromacs.bioexcel.eu/t/constant-ph-md/7901 "2023-12-21T11:26:49Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Jacopo](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jacopo/32/3635_2.png) [@Jacopo](https://gromacs.bioexcel.eu/u/Jacopo)\
**Post date:** [December 21, 2023, 11:26am UTC](https://gromacs.bioexcel.eu/t/constant-ph-md/7901/1 "2023-12-21T11:26:49Z")

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GROMACS version: 2021 and further  
GROMACS modification: Don’t know

Hi Everyone,

I’m currently trying to use the constant pH tool of gromacs. As reported in the GitLab tutorial:

> **[1\_ASP\_simulations/tutorial\_files/parameterisation/input\_files · main ·...](https://gitlab.com/gromacs-constantph/tutorials/-/tree/main/1_ASP_simulations/tutorial_files/parameterisation/input_files)**
>
> GitLab.com

You can find a " start\_param " script asking for the " md\_cph " mdp file. In the latter, I was wondering whether all the keywords/parameters reported under the “CONSTANT PH” comment line really exist in the gromacs versions from 2021 on.

Indeed, I show you here the way constant pH functionality has been announced (if you go back up to the “gromacs-constantph” directory): it refers the reader to the article " Scalable Constant pH Molecular Dynamics in GROMACS , J. Chem. Theory Comput. 2022, 18, 10, 6148–6160", where you can find the words “We have implemented the algorithms for CpHMD with charge  
interpolation in a fork of GROMACS software package (2021  
release).” So has that fork been merged in the main developing branch, or is it still under revision? In other words, if I download 2021+ versions, am I able to run the tutorial and make gromacs understand the cited keywords/parameters?

In fact, I read this statement " 2. Download the gromacs-constantph beta build. " in the following repository of the so called “phbuilder” tool:

> **[Gromacs constant ph / phbuilder · GitLab](https://gitlab.com/gromacs-constantph/phbuilder)**
>
> GitLab.com

which has been recenlty developed for automating the creation of constant pH files. The “beta build” words give me serious doubts …

For example, up to now I noticed that the 2019.3 version doesn’t read the parameters under the “CONSTANT PH” I cited. If I install the 2023 version, will those keywords be readable?

A last question: from the article of the abovementioned “phbuilder” : “phbuilder: a tool for efficiently setting up constant pH molecular dynamics simulations in GROMACS , ChemRxiv, 11 August 2023”, I understood that for non-coarse grained simulations, the only FF currently at disposal for running CpHMD is the charmm36m one: am I right? Indeed, the DOI reports: “Currently, the GROMACS constant pH implementation only supports  
a modified version of the charmm36m force field,” . I think this is a major limit of constant pH in gromacs with respect to competitors such as amber.

I kindly thank you for your interest, hope my issues will clarify the topic to others, too.

Best Regards,  
Jacopo