[Pw_forum] (no subject)

[vega lew]

Dear all,

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   
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/' ,
                      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,
                   celldm(3) = 2.5122,
                         nat = 12,
                        ntyp = 2,
                     ecutwfc = 30 ,
                     ecutrho = 240 ,
 /
 &ELECTRONS
                    conv_thr = 7.3D-8 ,
 /
 &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
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
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