Thanks for the help from Nicola and Charles.
vega
From: vega
Sent: Thursday, August 28, 2008 4:28 PM
To: PWSCF
Subject: [Pw_forum] something strange in rutile and anatase calculation
Dear all,
It is known that the rutile is more stable than anatase in thermodynamics.
Surprisingly, when I did the vc-relax calculation by QE, I found the calculated
energy of anatase lower than rutile. Both vc-relax calculation for rutile and
anatase onverged in 6 scf cycles and 3 bfgs steps, giving the final enthalpy =
-362.7585836890 Ry for rutile and -725.5447425835 Ry for antase. So the average
energy of [TiO2] unit is -181.3792918445 Ry for rutile and -181.386185645875 Ry
for anatase. It looks like anatase is more stable than rutile. Do you think it
was quite strange?
To make the calculation both for anatase and rutile comparable, I used the same
ecutwfc=40 Ry and ecutwfc=400 Ry, and a quite dense k-point mesh for both case,
4x4x7 for rutile and 5x5x2 for anatase.
for better understanding in my calculation, please read the input file below,
for anatase case,
&CONTROL
title = 'Anatase lattice' ,
calculation = 'vc-relax' ,
restart_mode = 'from_scratch' ,
outdir =
'/home/hjfeng/vega/TiO2/Anatase/lattice/vctest/tmp/' ,
wfcdir = '/tmp/' ,
pseudo_dir = '/home/hjfeng/vega/espresso-4.0/pseudo/' ,
prefix = 'Anatase lattice' ,
disk_io = 'none' ,
nstep = 1000 ,
/
&SYSTEM
ibrav = 6,
celldm(1) = 7.1356,
celldm(3) = 2.5122,
nat = 12,
ntyp = 2,
ecutwfc = 40 ,
ecutrho = 400 ,
/
&ELECTRONS
/
&IONS
ion_dynamics = 'bfgs' ,
/
&CELL
cell_dynamics = 'bfgs' ,
/
ATOMIC_SPECIES
Ti 47.86700 Ti.pw91-sp-van_ak.UPF
O 15.99940 O.pw91-van_ak.UPF
ATOMIC_POSITIONS crystal
Ti 0.000000000 0.000000000 0.000000000
Ti 0.500000000 0.500000000 0.500000000
Ti 0.000000000 0.500000000 0.250000000
Ti 0.500000000 0.000000000 0.750000000
O 0.000000000 0.500000000 0.042000000
O 0.000000000 0.000000000 0.208000000
O 0.500000000 0.500000000 0.292000000
O 0.000000000 0.500000000 0.458000000
O 0.500000000 0.000000000 0.542000000
O 0.500000000 0.500000000 0.708000000
O 0.000000000 0.000000000 0.792000000
O 0.500000000 1.000000000 0.958000000
K_POINTS automatic
5 5 2 1 1 1
for rutile case,
&CONTROL
title = Rutile_lattice ,
calculation = 'vc-relax' ,
restart_mode = 'from_scratch' ,
outdir = '/home/vega32/TiO2/rutile/lattice/vcrelax/tmp' ,
wfcdir = '/tmp/' ,
pseudo_dir = '/home/vega32/espresso-4.0.1/pseudo/' ,
prefix = 'Anatase lattice' ,
disk_io = 'none' ,
nstep = 1000 ,
/
&SYSTEM
ibrav = 6,
celldm(1) = 8.6814,
celldm(3) = 0.6441,
nat = 6,
ntyp = 2,
ecutwfc = 40 ,
ecutrho = 400 ,
/
&ELECTRONS
/
&IONS
ion_dynamics = 'bfgs' ,
/
&CELL
cell_dynamics = 'bfgs' ,
/
ATOMIC_SPECIES
O 15.99940 O.pw91-van_ak.UPF
Ti 47.90000 Ti.pw91-sp-van_ak.UPF
ATOMIC_POSITIONS crystal
O 0.304800000 0.304800000 0.000000000
O 0.695200000 0.695200000 0.000000000
O 0.195200000 0.804800000 0.500000000
O 0.804800000 0.195200000 0.500000000
Ti 0.500000000 0.500000000 0.500000000
Ti 0.000000000 0.000000000 0.000000000
K_POINTS automatic
4 4 7 1 1 1
vega
==============================================================
Vega Lew ( weijia liu)
PH.D Candidate in Chemical Engineering
State Key Laboratory of Materials-oriented Chemical Engineering
College of Chemistry and Chemical Engineering
Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
--------------------------------------------------------------------------------
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