The ABINIT Users Mailing List ( CLOSED )

[steeve.chretien@videotron.ca]

Dear Abinit users,

I am experienced VASP user trying to learn Abinit. I did all four tutorials but I still have some problems. I'll appreciate if someone could give me some hints.

I am trying to reproduce the experimental structure of Ag2O and AgO. With VASP, the lattice parameters are within 1% of the experimental values using the PBE functional, PAW pseudopotential, and a 2x2x2 Monkhorst-Pack grid. With Abinit 5.3.5, the lattice parameters are over estimated by at least 5% using the PBE functional and the Troullier-Martin (FHI-Berlin) optimized for PBE. The problem is not with the automatic optimization of the cell parameters (ioptcell=1) because they are overestimated as well when I performed a volume scan. I looked at the rutile TiO2 structure to see if the problem was related to the oxide. With VASP the lattice parameters are within 0.5% of the experimental values while the errors are ~3.5% with Abinit. Could the difference between VASP and Abinit due to pseudopotential? How can improve my calculations?

A typical input file for Ag2O looks like:

ndtset 4
prtkpt 1
kptopt 1
kptrlatt1  6  0  0    0  6  0    0  0  6
kptrlatt2 -4  4  4    4 -4  4    4  4 -4
kptrlatt3  8  0  0    0  8  0    0  0  8
kptrlatt4 -5  5  5    5 -5  5    5  5 -5
ACELL 3*4.72 Angstrom
RPRIM
1.000  0.000  0.000
0.000  1.000  0.000
0.000  0.000  1.000
NATOM       6
NTYPAT      2
TYPAT 4*1 2*2
ZNUCL 47 8
XRED
  0.250  0.250  0.250
  0.250  0.750  0.750
  0.750  0.750  0.250
  0.750  0.250  0.750
  0.000  0.000  0.000
  0.500  0.500  0.500
IXC        11
ECUT       15.0
NBAND      35
OCCOPT      7
TSMEAR      0.002
DIEMAC     12.0
ISCF        7
NPULAYIT   10
NSTEP      30
NSPPOL      1
TOLDFE      0.000001
ionmov   2
optcell  1

Thanks in advance,

All the best,

Steeve