Question on why single atom "energy without entropy" is very large

[bfax]

Dear VASP scientists and managers,

I have been using VASP 4.6 with PAW pseudopotentials (PPs). In the VASP book:

Hands on Session I:
Georg KRESSE
Institut f ?ur Materialphysik and Center for Computational Material Science
Universit?at Wien, Sensengasse 8, A-1090 Wien, Austria

I find the first example is to calculate a single oxygen atom. It is claimed on Page 13 that "the energy without entropy is essentially zero".

I have tried to calculate the energy of a Hf atom in a box:

*****INCAR*****
SYSTEM = Hafnium
ENCUT = 700
EDIFF = 1E-5
GGA = 91
VOSKOWN = 1
ISMEAR = 0
LPLANE = .TRUE.
NPAR = 1
NSIM = 4

*****POSCAR*****
Hafnium
1
15 0 0
0 15 0
0 0 15
1
Direct
0.5 0.5 0.5

*****KPOINTS*****
Gamma only
1
Reciprocal
0 0 0 1

And the POTCAR is a GGA(PW91) Hf_pv PAW PP.

I am surprised to find my
energy without entropy= -2.529233 eV

This makes me nervous since I expect it should be very near zero. I change another "Hf PAW pseudopotential" for LDA (this time NOT Hf_pv), and my corresponding LDA result is:
energy without entropy= -2.530314 eV

What is the reason that I got such large energy for a single atom? And if I do further calculation based on these, can I get correct energy difference all the time? I am not sure if I repeated above correctly the condition when these PPs were generated. If these PPs were generated in a different environment, probably it is merely a shift of zero point energy and I can cancel out the zero point energy (-2.5 eV) when I subtract two energies. Yet, I am not sure of whether this is the case, and would very much like to know the reason of -2.5 eV result (is it normal or not?).

Thank you very much!



<span class='smallblacktext'>[ Edited ]</span>

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