[Pw_forum] something strange in rutile and anatase calculation

[willy kohn]

Hi, Vega:

A recent result (Jpn. J. Appl. Phys. 39 (2000) L847) showed that different
pseudopotential leaded to different conclusions.

Best,

Wei

On Thu, Aug 28, 2008 at 4:28 AM, vega <vegalew at hotmail.com> wrote:

>  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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