NVE dynamics in i-pi

[Sriram Vignesh AK]

Hello everyone,

I want to perform NVE dynamics by giving excess energy to my reactant molecule(like say 50kcal/mol). How do I do this with the i-pi input?

For initialising NVE in i-pi it has option of giving momenta/velocities to be sampled at some temperature(using boltzmann dist), but I want to give a total energy and that energy to be distributed between the normal modes(microcanonical normal mode sampling) - Is there any in-built way to perform this in i-pi?

Thanks in advance

Sriram

[Venkat Kapil]

Hi Sriram, 

Thanks for your question.

You can do the following 

1. Optimise the molecule so that it is at its minimum energy structure
2. Estimate the kinetic energy that corresponds to the "excess energy" 
3. Estimate the temperature from the kinetic energy (noting the center of mass will be fixed by default in i-PI)
4. Provide that temperature in the input.xml file to i-PI.

This energy will be distributed to both the molecule's normal modes and its rotational degrees of freedom. 

Here is a sample input for NVE dynamics: https://github.com/venkatkapil24/MLIPs-with-iPI/blob/main/00-NVE/input.xml

Kind regards,
Venkat