Constrained dynamics with NPT

[omm...@udel.edu]

Hi all,

I would like to run NPT simulations in the classical approximation (nbeads = 1) using my own driver, which provides energies, forces, and virials for a constrained system (rigid water). I noticed that i-PI's <mode>constrained</mode> only supports NVE and NVT ensembles. Is there a recommended way to perform NPT simulations with rigid-body dynamics handled entirely by the driver?

Best

O

[Mariana Rossi]

Hello,

Happy to hear you are trying i-PI out. I am not aware that i-PI can apply holonomic constraints for any type of dynamics at the moment (not only NVT), but perhaps @ceriotti can add here.

However, I think it should still be possible to run dynamics with rigid water molecules - I am not the experienced one on this front. 

[Michele Ceriotti]

There is an implementation of constraints but it has never been used in production and is not very well tested.

Most definitely won't allow you to do PIMD with constraints which is its own beast. If you have any level of 

expertise on this front and want to contribute, checking and polishing the existing implementation (and 

maybe adding an example) would be very much welcome.

M

[omm...@udel.edu]

Thank you, Prof. Michele, for the clear explanation. I will review the code and see if I can adapt it to my needs. I have experience implementing rigid body dynamics using the quaternion algorithm. If I’m able to successfully integrate the quaternion-based approach with the i-PI framework, I will prepare a working example to share.