[Pw_forum] ground state structure calculation -reg.,

[Suresh A]

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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