Free, isolated atom calculation

[zsoltrak]

Does it make sense to perform LDA+U/GGA+U calculation on a free, isolated transition metal atom. If I do GGA+U on Ni atom, with the INCAR below, I get positive total energy. What am I doing wrong? (The energy without entropy is also positive)

Thanks,
Zsolt

The INCAR:
System = Ni atom
ISTART = 1
ICHARG = 1
ENCUT = 560
PREC = High

ISPIN = 2
#MAGMOM = 2

ISMEAR = 0
SIGMA = 0.05

#FERWE = 3*1 5*1 1 7*0
#FERDO = 3*1 3*1 2*0 1 7*0

EDIFF = 0.0001
NELM = 440
#AMIX = 0.2 # mixing set manually
#BMIX = 0.0001


LDAU=.True.
LDAUTYPE = 2
LDAUPRINT = 1
LDAUL = 2
LDAUU = 5.1
LDAUJ = 0.0

#LREAL = Auto

LPLANE = .True.
NPAR = 16 ! number of nodes.
NSIM = 4

LSCALU = .FALSE.

LMAXMIX = 4
MAXMIX = 40

ISYM = 0

[alex]

Hi zsoltrak,

I'd say something went terribly wrong in your calculation. It should become negative. Have you checked, if the occupation is all right?

Cheers,

alex

[zsoltrak]

Thank you for your comment Alex, however, my question is still unanswered: does it make sense to carry out DFT+U calculation on free atoms? Yes, I checked the occupations; in fact I tried numerous fixed occupations and also continuation of the calculation keeping the GGA occupations fixed. Any suggestions...?

Thanks,
Zsolt

[Neutrino]

Hi Alex and Zsolt,


The positive energy with DFT+U should be fine. Negative energies are typically obtained with the functional via which the pseduopotential was generated. Any modification of this functional somehow such as adding U or superimposing a different one (e.g. AM05 on top of PBE pseudo) will certainly change the absolute total energy of the free atom.

Anyways absolute total energies energies are meaningless.


Mostafa