[Pw_forum] Anatase lattice parameters testing results

[Charles Chen]

vega lew wrote:
> Dear all,
>
> There is someting wrong with last mail, so I send it again.
>
> Now I have tested Anatase lattice parameters using new BFGS file of
> PWscf. The new BFGS files
> seem to be perfect. The data in following table is calculated by PWscf
> except for the first two lines.
> The first line is the experimental data at 15K of J. Am. Chem. SOC.
> 1987, 109, 3639-3646.
> The second line is the average value calculated by CASTEP. But the
> value is not stable, it's
> would be changed a bit of different run.
> From the third line to the bottom is the data calculated by PWscf. The
> value is quite stable.
> The value remain the same when calculate by same number of CPUs and
> pools. There would
> be only a little different for different number of CPUs and pools,
> less than 0.01% in energy.
>
> K-point mesh Pseudopotentials Cutoff / Ry Anatase lattice parameters time
> a=b c Energy / Ry CPU Wall
> experiment* x 3.78216 9.50465 x x x
> CASTEP 400 eV 3.7987 9.6934 -730.11745
> gamma (1X1X1) 30,240 3.39021 11.77804 -725.08174 4m18.70s 18m 9.12s
> 2X2X1 30，240 3.8683 9.0275 -725.48834 8m 4.25s 32m33.56s
> 4X4X2 25,200 3.7500 9.3829 -725.41398 9m58.82s 17m46.87s
> 30,240 3.7899 9.6203 -725.49520 3m41.55s 7m50.32s
> 40,320 3.7850 9.5716 -725.54336 8m54.73s 34m 1.43s
> 50,400 3.7926 9.6366 -725.59434 10m14.46s 41m 3.22s
> 7X7X3 30,240 3.7919 9.6058 -725.49443 31m59.60s 46m37.77s
> 10X10X4 30,240 3.7916 9.6067 -725.49451 31m32.94s 44m 4.11s
I bet you did not check force convergence wrt ecutwfc, ecutrho, and MP
grid. I would rather have a more systematic convergence test.

Another point is, anatase is in space group I41/amd or ibrav=7. Of
course this will not make much difference as you use ibrav=6
>
> The input file as follows,
>
> &CONTROL
> title = 'Anatase lattice' ,
> calculation = 'vc-relax' ,
> restart_mode = 'from_scratch' ,
> outdir = '/home/vega/espresso-4.0/tmp/' ,
> wfcdir = '/tmp/' ,
> pseudo_dir = '/home/vega/espresso-4.0/pseudo/' ,
> &n! bsp; prefix = 'Anatase lattice default' ,
> disk_io = 'none' ,
> etot_conv_thr = 0.0005 ,
> forc_conv_thr = 0.0011668141375 ,
> nstep = 1000 ,
> /
> &SYSTEM
> ibrav = 6,
> celldm(1) = 7.1356,
> ! ; &nb sp; celldm(3) = 2.5122,
> nat = 12,
> ntyp = 2,
> ecutwfc = 30 ,
> ecutrho = 240 ,
> /
> &ELECTRONS
> conv_thr = 7.3D-8 ,
> /
> &IONS
> ion_dynamics = 'bfgs' ,
> /
> &CELL
> &nbs! p; 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
> &n! bsp; O 0.500000000 &nbs p; 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
> 2 2 1 1 1 1
>
> But it is especially strange that the total energy was -730.11745 Ry,
> rather different than the PWscf's results.
> Also PWscf's results seems to be a litter lager than experimental
> data. Is it because the pseudopotential Ti.pw91-sp-van_ak.UPF
> underbinding! for TiO2?
>
>
> Vega Lew
> 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
> Vega Lew
> 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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