mjv500
commented
4 months ago Hi Rashid,
no - in a word. Olle convinced me there are some pretty fundamental issues which impose using NVT simulations for TDEP, and it's best to do several different volume NVTs rather than mess with the NPT. The indexing of the atoms and the reference positions are not well defined, so the displacements to match the forces and stress are not uniquely defined either.
What we do is NPT to get equilibrated volumes for the T we want, then stop and run an NVT from a well thermalized starting point. This is all easier with an MLIP of course, with explicit DFT you are better off doing canonical configurations, then adjusting the full Free energy in the V-T space to find the equilibrium volume etc. You can get Gibbs from F or H doing the appropriate thermodynamic transforms.
Best
Matthieu
On Thu, Jun 27, 2024 at 1:10 PM Rashid Rafeek @.***> wrote:
This is a question on the TDEP method itself, and might not be applicable to the tdep code. But I thought this might be a good place to ask this question. Please let me know if it not.
I was wondering whether NPT simulations, where the volumes are fluctuating can be used to fit the IFCs. I noticed that the TDEP formalism is developed for constant volume simulations. And in the publications generally several NVT simulations at different volumes are done to obtain the pressure and thereby the Gibbs Free energy. For example, it is mentioned in this publication https://pubs.acs.org/doi/full/10.1021/acs.jpca.6b08633 that,
Though it is possible to carry out simulations in the NPT ensemble, they are currently not well suited for use with the TDEP method because the underlying formalism assumes a constant volume when fitting results of the MD simulation to obtain the force-constant matrix
Is this the only way to compute the Gibbs Free energy? Is there any alternative to this method if I only have NPT simulations? Any information regarding this would be useful. Thanks.
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rashidrafeek
This is a question on the TDEP method itself, and might not be applicable to the tdep code. But I thought this might be a good place to ask this question. Please let me know if it not.
I was wondering whether NPT simulations, where the volumes are fluctuating can be used to fit the IFCs. I noticed that the TDEP formalism is developed for constant volume simulations. And in the publications generally several NVT simulations at different volumes are done to obtain the pressure and thereby the Gibbs Free energy. For example, it is mentioned in this publication that,
Is this the only way to compute the Gibbs Free energy? Is there any alternative to this method if I only have NPT simulations? Any information regarding this would be useful. Thanks.