Dear All,
I am a newer to use Quantum Espresso. Could you please do me a favor to answer
some little questions I met when using Quantum Espresso?
1. I am investigating the BaTiO3 crystal and used the best optimized parameter
a=7.5344 Bohr. I used 'scf' to calculate the total energy. However, I obtained
different values when using different number of cells. For example, when I use
the unit cell, the total energy is -304 Ry, but when I use 1X1X2? supercell, I
obtained E=-598Ry, i.e., -299Ry per unit cell, when I increased to 2X2X4
supercell (the input file is below these questions), I got E=-4766Ry, i.e.,
-298 Ry per unit cell. What is wrong?
2. Another strange result is when I?replaced two Ti atoms (Ti4+)?by two Fe
atoms (Fe3+) and removed one O atom (O2-)?between them in the 2X2X4 supercell,
I obtained even lower energy than the pure BaTiO3 crystal. What is wrong? It
isnot reasonable, right?
3. I use the atom pseudopotential file, but Ba4+ or Fe3+ are both ions, should
I?generate?their ionic pseudopotential files?
Following is my input file.
&control
calculation = 'scf',
prefix = 'BaTiO3',
pseudo_dir='/work/01553/geng'
/
&system
degauss=0.01
ibrav=6
celldm(1)=15.0688
celldm(3)=2
nat=80
ntyp=3
ecutwfc=30.0
ecutrho=300.
/
&electrons
conv_thr = 1e-5,
mixing_beta=0.7
/
&IONS
ion_dynamics='bfgs',
/
&CELL
cell_dynamics='damp-w',
/
ATOMIC_SPECIES
Ba 137.327 Ba.pbe-nsp-van.UPF
Ti 47.867 Ti.pbe-sp-van_ak.UPF
O 15.9994 O.pbe-van_ak.UPF
ATOMIC_POSITIONS
Ba 0.000 0.000 0.000
Ba 0.000 0.000 0.250
Ba 0.000 0.000 0.500
Ba 0.000 0.000 0.750
Ba 0.500 0.000 0.000
Ba 0.000 0.500 0.000
Ba 0.500 0.500 0.000
Ba 0.500 0.000 0.250
Ba 0.500 0.000 0.500
Ba 0.500 0.000 0.750
Ba 0.000 0.500 0.250
Ba 0.000 0.500 0.500
Ba 0.000 0.500 0.750
Ba 0.500 0.500 0.250
Ba 0.500 0.500 0.500
Ba 0.500 0.500 0.750
Ti 0.250 0.250 0.125
Ti 0.250 0.250 0.375
Ti 0.250 0.250 0.625
Ti 0.250 0.250 0.875
Ti 0.750 0.250 0.125
Ti 0.750 0.250 0.375
Ti 0.750 0.250 0.625
Ti 0.750 0.250 0.875
Ti 0.250 0.750 0.125
Ti 0.250 0.750 0.375
Ti 0.250 0.750 0.625
Ti 0.250 0.750 0.875
Ti 0.750 0.750 0.125
Ti 0.750 0.750 0.375
Ti 0.750 0.750 0.625
Ti 0.750 0.750 0.875
O 0.250 0.000 0.125
O 0.250 0.000 0.375
O 0.250 0.000 0.625
O 0.250 0.000 0.875
O 0.750 0.000 0.125
O 0.750 0.000 0.375
O 0.750 0.000 0.625
O 0.750 0.000 0.875
O 0.000 0.250 0.125
O 0.000 0.250 0.375
O 0.000 0.250 0.625
O 0.000 0.250 0.875
O 0.000 0.750 0.125
O 0.000 0.750 0.375
O 0.000 0.750 0.625
O 0.000 0.750 0.875
O 0.250 0.500 0.125
O 0.250 0.500 0.375
O 0.250 0.500 0.625
O 0.250 0.500 0.875
O 0.750 0.500 0.125
O 0.750 0.500 0.375
O 0.750 0.500 0.625
O 0.750 0.500 0.875
O 0.500 0.250 0.125
O 0.500 0.250 0.375
O 0.500 0.250 0.625
O 0.500 0.250 0.875
O 0.500 0.750 0.125
O 0.500 0.750 0.375
O 0.500 0.750 0.625
O 0.500 0.750 0.875
O 0.250 0.250 0.000
O 0.250 0.250 0.250
O 0.250 0.250 0.500
O 0.250 0.250 0.750
O 0.750 0.250 0.000
O 0.750 0.250 0.250
O 0.750 0.250 0.500
O 0.750 0.250 0.750
O 0.250 0.750 0.000
O 0.250 0.750 0.250
O 0.250 0.750 0.500
O 0.250 0.750 0.750
O 0.750 0.750 0.000
O 0.750 0.750 0.250
O 0.750 0.750 0.500
O 0.750 0.750 0.750
?
K_POINTS {automatic}
20 20 10 0 0 0
Thank you very much!
Best regards,
Liwei
?
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