pressure and temperature

General discussion of the Cambridge quantum Monte Carlo code CASINO; how to install and setup; how to use it; what it does; applications.
Post Reply
Subhodip_Chatterjee
Posts: 4
Joined: Tue Apr 21, 2015 12:39 pm
Location: Kolkata, India

pressure and temperature

Post by Subhodip_Chatterjee »

Hi all,
I'm new in CASINO and I'm trying to learn by going through the manual. I want to know that can pressure and temperature be introduced in qmc calculations using CASINO??

Best Regards,
Subhodip
Neil Drummond
Posts: 113
Joined: Fri May 31, 2013 10:42 am
Location: Lancaster
Contact:

Re: pressure and temperature

Post by Neil Drummond »

Dear Subhodip,

VMC and DMC are zero-temperature methods that work in fixed simulation cells.

If you want to calculate the equation of state of a solid then you need to calculate the DMC energy as a function of cell volume E(V). The static-lattice pressure at zero temperature can then be evaluated as p=-dE/dV. Typically this is done by fitting a model equation of state (e.g., Vinet or Birch-Murnaghan) to your set of E(V) points.

If you want to study finite temperatures then you need to add in the Helmholtz free energy of phonon vibrations to each of your static-lattice energies. These would normally be taken from DFT phonon calculations. You then have F(V,T), from which you can find the temperature-volume-pressure equation of state as p(V,T)=-dF/dV.

One can also calculate the pressure more directly but usually less accurately from QMC kinetic and potential energies using the virial theorem.

Best wishes,

Neil.
Subhodip_Chatterjee
Posts: 4
Joined: Tue Apr 21, 2015 12:39 pm
Location: Kolkata, India

Re: pressure and temperature

Post by Subhodip_Chatterjee »

Thanks Neil...
Post Reply