Computing electronic free energy
Posted: Fri Sep 28, 2012 7:52 pm
Good afternoon,
I am working with a program which takes in an electronic density of states (DOS) file generated by VASP and then computes the electronic free energy F:
F=E-TS,
by using the DOS data. It does so by using integrals over the DOS with the Fermi-Dirac distribution, e.g. the internal mean energy in a heat bath at temperature T is:
<E> = int E*g(E)*f(E,T)*dE, where f(E,T) is the Fermi-Dirac distribution and g(E)*dE is the number of states per unit cell (as output from VASP).
The entropy is similarly computed using the DOS data.
My questions are:
1) The "total energy" as computed by VASP is that the total eletronic energy computed from the integral stated above?
In other words: If I have the output energy from VASP do I need to compute the electronic energy using the DOS or is that just redundant work?
2) Does VASP output electronic entropy?
If so, then I don't see why this program uses the DOS instead of the data given directly by VASP. Or am I missing something?
Thank you.
I am working with a program which takes in an electronic density of states (DOS) file generated by VASP and then computes the electronic free energy F:
F=E-TS,
by using the DOS data. It does so by using integrals over the DOS with the Fermi-Dirac distribution, e.g. the internal mean energy in a heat bath at temperature T is:
<E> = int E*g(E)*f(E,T)*dE, where f(E,T) is the Fermi-Dirac distribution and g(E)*dE is the number of states per unit cell (as output from VASP).
The entropy is similarly computed using the DOS data.
My questions are:
1) The "total energy" as computed by VASP is that the total eletronic energy computed from the integral stated above?
In other words: If I have the output energy from VASP do I need to compute the electronic energy using the DOS or is that just redundant work?
2) Does VASP output electronic entropy?
If so, then I don't see why this program uses the DOS instead of the data given directly by VASP. Or am I missing something?
Thank you.