# Tau values for equilibration **URL:** \ **Category:** User discussions\ **Tags:** mdp-parameters, simulation-setup\ **Created:** [January 8, 2025, 12:55pm UTC](https://gromacs.bioexcel.eu/t/tau-values-for-equilibration/10975 "2025-01-08T12:55:17Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![mostafagh98](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mostafagh98/32/4214_2.png) [@mostafagh98](https://gromacs.bioexcel.eu/u/mostafagh98)\ **Post date:** [January 8, 2025, 12:55pm UTC](https://gromacs.bioexcel.eu/t/tau-values-for-equilibration/10975/1 "2025-01-08T12:55:17Z")
GROMACS version: 2019 GROMACS modification: No Hi everyone, I’m running a simulation of a peptide in water and have a few questions about setting up the MDP parameters. Just to note, I’m using the V-rescale thermostat and C-rescale barostat. From what I’ve seen on the forums, the recommended values for tau\_t are 1 ps and tau\_p are 5 ps. > [@What is the recommended value for tau-p and tau-t with GROMACS2023.0 when using PR and NH](https://gromacs.bioexcel.eu/t/what-is-the-recommended-value-for-tau-p-and-tau-t-with-gromacs2023-0-when-using-pr-and-nh/5840/3): > > Thank you very much for your insightful answer! Yes, I meant picoseconds not nanoseconds. Perfect than I will try v-rescale as a thermostat and c-rescale as a barostat. For the combination of v-rescale as thermostat and c-rescale as barostat is there any condition for the ratio of tau\_p/tau\_t that needs to be fulfilled (such as tau\_p \>= 2\* tau\_t when using NH and PR)? I would really like to use the increased values for nsttcouple and nstpcouple so I would increase my tau\_p and tau\_p value re… As far as I understand, these values are for the production run. Are they suitable for a small system with a 30-amino-acid peptide? I’ve also come across studies where tau\_p = 2 was used. Also, if these values are for production, what should be the values for equilibration? Should they be smaller? For example, I’ve seen tau\_t = 0.1 used during NVT equilibration. Thanks in advance to anyone who responds! ---
**Author:** ![MagnusL](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/magnusl/32/2380_2.png) [@MagnusL](https://gromacs.bioexcel.eu/u/MagnusL)\ **Post date:** [January 9, 2025, 7:56am UTC](https://gromacs.bioexcel.eu/t/tau-values-for-equilibration/10975/2 "2025-01-09T07:56:11Z")
Those values should be suitable for a small peptide as well, yes. Basing your values on other studies _might_ not be very good (unless you are trying to reproduce them), since previous poor choices of parameters may remain in use for no good reason. You should know why you choose the settings you use. In general, you can use a lower tau\_t for equilibration, to have a stricter control of the temperature. You would usually be able to use a lower tau\_p as well, but setting it too low may make the simulation unstable, even when using first order coupling algorithms. I would think that tau\_t between 0.5 and 2 ps and tau\_p between 2 and 10 ps (with a c-rescale barostat) would work for most atomistic systems. But is there a specific reason why you think you need to set them lower than 1 and 5 ps, respectively? ---
**Author:** ![mostafagh98](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mostafagh98/32/4214_2.png) [@mostafagh98](https://gromacs.bioexcel.eu/u/mostafagh98)\ **Post date:** [January 9, 2025, 8:15am UTC](https://gromacs.bioexcel.eu/t/tau-values-for-equilibration/10975/3 "2025-01-09T08:15:23Z")
Thank you for your valuable insight! I’ve often seen tau\_p = 5 ps used for larger systems, such as membranes or proteins, which led me to hypothesize that it might not be optimal for smaller systems like peptide simulations. However, I’ve understood that first-order coupling algorithms are less sensitive to tau values, which makes this less of a concern. ---
**Author:** ![MagnusL](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/magnusl/32/2380_2.png) [@MagnusL](https://gromacs.bioexcel.eu/u/MagnusL)\ **Post date:** [January 9, 2025, 8:44am UTC](https://gromacs.bioexcel.eu/t/tau-values-for-equilibration/10975/4 "2025-01-09T08:44:17Z")
Large systems usually have a more stable pressure, so I would _think_ that smaller systems might need a higher tau\_p, rather than lower, if it would need to be changed at all. But I might be wrong in that assumption.