Dear all
?
I calculated the lattice constant of BaTiO3 using GGA. However, the calculated
lattice constant ( 3.980 angstrom) is SMALLER than experimental results (4.012
angstrom). So is this result reasonable?
?
The?GGA results of SrTiO3 is ok, 3.928 angstrom?vs expermental result ?3.905.
As SrTiO3 and BaTiO3 both contain Ti and O,?I calculated lattice constant of
bulk metal Ba as a test, and the?GGA results (5.014 angstrom for bcc cell) is
also?smaller than experimental one (5.019).
?
So is there something?wrong with my calculation? Or GGA does underestimate the
lattice constant of some metals, such as reported in Computer Coupling of Phase
Diagrams and Thermochemistry 28(2004)79-90 ?
?
The input file is attached below. Thank you very much for your help
Ruizhi?
===========input file of BaTiO3===============
&control
??? calculation? = 'vc-relax'
??? restart_mode = 'from_scratch'
??? prefix = 'bto'
??? pseudo_dir?? = '~/pseudo/'
??? outdir?????? = './tmp/'
?/
?&system
??? ibrav=1
??? celldm(1)=7.584
??? nat=5
??? ntyp=3
??? ecutwfc=30.0
??? occupations = 'smearing'
??? degauss=0.01
?/
?&electrons
??? conv_thr = 1e-8
??? mixing_beta=0.3
?/
&IONS
? ion_dynamics = 'damp',
?/
?&CELL
? cell_dynamics ='damp-pr'
?
?/
ATOMIC_SPECIES
? Ba??? 137.33? Ba.pbe-nsp-van.UPF
? Ti??? 47.90?? Ti.pbe-sp-van_ak.UPF
? O???? 15.99?? O.pbe-van_ak.UPF
ATOMIC_POSITIONS (crystal)
? Ba??? 0.000??? 0.000??? 0.000
? Ti??? 0.500??? 0.500??? 0.500
? O???? 0.000??? 0.500??? 0.500
? O???? 0.500??? 0.500??? 0.000
? O???? 0.500??? 0.000??? 0.500
K_POINTS {automatic}
? 8 8 8 1 1 1
=============end input file=============
========================
Ruizhi Zhang, PhD
School of Physics,Shandong University
Jinan, Peopel's Republic of China
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