A question about the EATOM in POTCAR

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dyc_2008 · #1 Post by **dyc_2008** » Tue Nov 29, 2011 6:09 am

dear all,

In the POTCAR of H， I read the following：

PAW_PBE H 15Jun2001
1.00000000000000000
parameters from PSCTR are:
VRHFIN =H: ultrasoft test
LEXCH = PE
EATOM = 12.4884 eV, .9179 Ry

And，in the manual，I read this：
The POTCAR files also contain information on the energy of the atom in the reference configuration.

In my opinion, the ground state energy of H is -13.6ev.
but the EATOM = 12.4884 eV.
a. Is EATOM (+ 12.4884 eV) or )- 12.4884 eV) ?
b. In this case , what is the reference configuration?

thank you so much

tlchan · #2 Post by **tlchan** » Mon Dec 05, 2011 8:03 am

[quote author= 12.4884 eV.
a. Is EATOM (+ 12.4884 eV) or )- 12.4884 eV) ?
[/quote]
Probably EATOM quotes the absolute magnitude of the total energy. Hydrogen has 1 electron. Under the DFT formalism, the electron self-interacts with itself via the Hartree potential. It is supposed that the exchange energy can cancel the self-interaction energy; however, the cancellation is not exact leading to higher total energy for the hydrogen atom than expected.

dyc_2008 · #3 Post by **dyc_2008** » Mon Dec 05, 2011 8:28 am

thank you so much
tlchan