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First-principles statistical mechanical software for the study of multi-component crystalline solids
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Formation energy differences at 0K CE and finite-T MC #259

Open sjtuzhanglei opened 2 years ago

sjtuzhanglei commented 2 years ago

Dear CASM developers,

I found that although the formation energies at 0K CE are zero for two end members (as they are set as references), the ones generated from finite-T MC are not.

I can understand that for one end member, finite-T excites more configurations so that its formation energy is non-zero and increasing with the temperature; but for the other one, BaZrO3, there is a finite and constant value across the temperature within MC simulations. Wondering what energy contribution is taking into account at finite-T in MC simulations, that make its formation energy non-zero?

And for the formation energy generated for the middle compositions, is it the 0K enthalpy + configuration entropy that used to subtract the 0K enthalpy + configuration entropy of two end members? The details is not clear for me. Please help clarify and appreciate your response!

Thanks,

sjtuzhanglei commented 2 years ago

OK, I think I know the finite formation energy value is from the fitting value of ECI, not DFT references. name selected comp(a) formation_energy clex(formation_energy) BaZrO3 SCEL1_1_1_1_0_0_0/6 1 0.00000000 0.00000000 0.01828650

Now my question is in MC run, How the energy for the middle solid solutions is calculated? by the statistical average of enthalpy (0K) through partition function, or a 0K ECI evaluation under MC equilibrated structure? How is the temperature effect playing in the role here?

bpuchala commented 2 years ago

The Monte Carlo results "" values are the average value of X taken from observations occurring after equilibriation is detected. The output includes the number of observations included in the averaging, and the number taken during equilibration. All individual observations can be requested for output also. Temperature makes states with higher formation energy more likely to occur.

sjtuzhanglei commented 2 years ago

Will there be any difference (theoretically and numerically) between a simulated annealing down to room temperature and a fixed-T MC at the room temperature?

sjtuzhanglei commented 1 year ago

I guess my question is: the MC finite-T formation_energy is the total energy of arbitrary composition minus the 0 K energy of end-member, or the corresponding finite-T energy of end-member?

Given that the end-member still has configurations, the energy goes up w.r.t increasing temperature.

Thanks,