[Pw_forum] ground state structure calculation -reg.,

[Savaş]

    Dear Suresh,

    Variable-cell-shape geometry optimization is quite stable in QE and
    free from human errors caused by ignorance or wrong implementation
    of some necessary steps in hand calculations which takes our 
valuable time.
    Beside in QE you need not worry about symmetry conservation (unlike 
SIESTA :
    in siesta you should write your own routine to massage strains). A 
year ago I was
    trying to determine lattice parameters of \alpha-Uranium  and qe's 
accuracy
    was in line between experimental and full-potential values.

    Note that initial guess for lattice paramaters is important but even 
for bad
    guess (some degree, of course!) their code is smart enough on choosing
    right direction within optimization process.

    Savaş AĞDUK
    Research Assistant
    Karabuk University
    Physics Department

On 11/06/2013 01:29 PM, Suresh A wrote:
> I am new to QE. I have done variable cell volume optimization for 
> rutile tio2.
> I confused with finding ground state structure.
>
> In literature survey the authors did volume- constraint total energy 
> minimization and have set cell parameters a, c and internal 
> parameter(  u for rutile)
> finally fitted their value Birch - Murnaghan equation(B-M) . From the 
> final value they have compared their values with exprimental values of 
> cell parameter
> a,c and elastic parameters.
>
> my question is:
>
>  i) which method is correct whether doing doing vc-relax alone  or 
> collect all volume and total energy from vc-relax output and fitting 
> this with B-M  equation ?
>
>  ii) How to choose internal parameter u for TiO2 rutile.?
> i have included the input file.
>
>  &CONTROL
>                        title = 'rutile' ,
>                  calculation = 'vc-relax' ,
>                 restart_mode = 'from_scratch' ,
>                       outdir = '/home/basheer/Desktop/relax/' ,
>                   pseudo_dir = '/home/basheer/espresso-5.0.1/pseudo/' ,
>                       prefix = 'rutile' ,
>                etot_conv_thr = 1.d-6 ,
>                forc_conv_thr = 1.d-4 ,
>                      tstress = .true. ,
>                      tprnfor = .true. ,
>  /
>  &SYSTEM
>                        ibrav = 6,
>                            A = 4.59373 ,
>                            B = 4.59373 ,
>                            C = 2.95812 ,
>                        cosAB = 0 ,
>                        cosAC = 0 ,
>                        cosBC = 0 ,
>                          nat = 6,
>                         ntyp = 2,
>                      ecutwfc = 200 ,
>                      ecutrho = 800 ,
>                  occupations = 'smearing' ,
>                      degauss = 0.01 ,
>                     smearing = 'gaussian' ,
>             exxdiv_treatment = 'gygi-baldereschi' ,
>  /
>  &ELECTRONS
>                     conv_thr = 1.d-12 ,
>  /
>  &IONS
>  /
>  &CELL
>                cell_dynamics = 'bfgs' ,
>               press_conv_thr = 2 ,
>  /
> ATOMIC_SPECIES
>    Ti   47.88800  Ti.pz-mt_fhi.UPF
>     O   15.99900  O.pz-mt_fhi.UPF
> ATOMIC_POSITIONS angstrom
>    Ti      0.000000000    0.000000000 0.000000000
>    Ti      2.296860000    2.296860000 1.479060000
>     O      1.402470000    1.402470000 0.000000000
>     O      3.191260000    3.191260000 0.000000000
>     O      0.894400000    3.699330000 1.479060000
>     O      3.699330000    0.894400000 1.479060000
> K_POINTS automatic
>   4 4 4   1 1 1
>
>
>
> A.Suresh,
> Project Fellow,
> Madurai Kamaraj University,
> Madurai.
>
>
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