I try to compute cohesive energy (Ecoh) and equilibrium distance (req) of Ga-N dimer. From previous computations I have results of N-N and Ga-Ga dimers which are consistent with references. But I still have wrong results for Ga-N dimer (Ecoh = 0.8eV ref. 2.4eV, req = 1.75A ref. 1.9A). The best results (according to references) I have got in run with spin polarized option (nsppol 2 - script attached) - Ecoh = 2.3eV, req = 1.75A.
Cohesive energy is computed with total energies of single atoms Ga/N in the box with the same dimensions.
All calculations were done with norm-conserving pseudopotentials from abinit webpage (https://www.abinit.org/psp-tables - Ga.psp8, N.psp8).
Thank you for any advise
Code: Select all
# Ga-N
# Structural optimalization of Ga-N dimer bonding distance
ndtset 3
acell 32 32 32 # dimensions of the empty box
ecut 50 # maximal kinetic energy cut-off [Ha]
# First dataset: dimer Ga-N
natom1 2 # there are two atoms in the unit cell
occopt1 3
ionmov1 2 # can move freely
tsmear1 0.001
xred1 0.45 0.0 0.0 # The starting values of the
0.55 0.0 0.0 # atomic coordinates
nband1 14
typat1 1 2 # these are Ga N
# Second dataset: single atom of Ga
natom2 1 # there is one atom in the unit cell
occopt2 2 # Allow occupation numbers to be set by hand
nband2 7 6 # Number of bands for spin up and spin down -----> in valence 4 spin up a 1 spin down
occ2 1 1 1 1 1 1 1 # Occupation numbers for spin up state and spin down state. ---> 1st row spin up, 2nd row spin down
1 1 1 1 1 1 0 # dimensions (nband(1)+nband(2)+...+nband(nkpt))*nsppol
xred2 0.5 0.0 0.0 # The starting values
nsym2 1 # not spherical symmetry
spinat2 0.0 0.0 1.0 # Initialisation of spin
typat2 1 # This is Ga
# Third dataset: single atom of N
natom3 1 # there is one atom in the unit cell
occopt3 2 # Allow occupation numbers to be set by hand
nband3 4 1 # Number of bands for spin up and spin down -----> in valence 4 spin up a 1 spin down
occ3 1 1 1 1 # Occupation numbers for spin up state and spin down state. ---> 1st row spin up, 2nd row spin down
1 # dimensions (nband(1)+nband(2)+...+nband(nkpt))*nsppol
xred3 0.5 0.0 0.0 # The starting values
nsym3 1 # not spherical symmetry
spinat3 0.0 0.0 1.0 # Initialisation of spin
typat3 2 # This is N
#-----------------------------------------------------------------
nsppol 2 # Spin polarized calculation
ntypat 2 # # of atom types
znucl 31 7 # atomic numbers of Ga and N
ntime 500 # max number of iteration
optcell 0 # acell cannot change
tolmxf 1.0d-4 # Stopping criterion for the geometry optimization
# SCF calculation parameters
toldfe 1.0d-4 # stopping criteria for SCF
nstep 500 # maximal number of SCF cycles
# Definition of K-points
kptopt 0 # Enter the k points manually
nkpt 1 # Only one k point is needed for isolated system,
# taken by default to be 0.0 0.0 0.0
diemac 2.0 # macroscopic dielectric constant (speeds up SCF calculations)