OUTCAR question

[hansonr]

The question I have is this: Given the OUTCAR report extract shown below, would the following be true?

G = 35.37614365
H = 35.38870300
TS = 0.01255935

such that

G = H - TS

If so, why is the TS listing negative? If not, what am I missing? Is that "T*S" really referring to "-T*S"?

Thank you.



Free energy of the ion-electron system (eV)
---------------------------------------------------
alpha Z PSCENC = 2.19859438
Ewald energy TEWEN = -190.65579816
-1/2 Hartree DENC = -11.64936915
-V(xc)+E(xc) XCENC = -37.58169861
PAW double counting = 71.42637628 -7.53723064
entropy T*S EENTRO = -0.01255935
eigenvalues EBANDS = 27.21110509
atomic energy EATOM = 181.97672381
---------------------------------------------------
free energy TOTEN = 35.37614365 eV

energy without entropy = 35.38870300 energy(sigma->0) = 35.38242333

[alex]

No. Your energy is positive, so your calculation is probably totally wrong. TS in the OUTCAR is only the electronic entropy caused by smearing (correct?).
To get the complete TS you need to calculate partition sums (via a frequency calculation). This is nicely explained in the Gaussian whitepaper Thermochemistry: http://www.gaussian.com/g_whitepap/thermo.htm

Cheers,

alex

[admin]

you are correct, alex.
also, the thermodynamic potentials as written in VASP are not G and H, but F (TOTEN) and U (energy without entropy).

[hansonr]

Ah, yes, sure -- G/A(F), H/E(U). That's fine. Then I'll rephrase my question:

The OUTCAR report gives:

entropy T*S EENTRO = -0.01255935
free energy TOTEN = 35.37614365 eV
energy without entropy = 35.38870300

Now, these three values do add up:

TOTEN = "energy without entropy" + EENTRO

But it would seem to me that

TOTEN = F
"energy without entropy" = U
"EENTRO" = TS (as stated in the table)

But the equation is

F = U - TS

not

F = U + TS

So is that EENTRO table entry really -TS?

Thanks,

Bob Hanson

(sorry for the delay --- I was expecting an email alert on this and didn't get it -- I will check my forum settings....)