[Pw_forum] Volume Optimisation :-Reg

[Suresh A]

Dear All,
            I have optimized the structure for anatase simple tetragonal.
The optimiized lattice parameters are a= 3.754336A. c=9.193631522694A. but
the experimental values are a= 3.785A, c=9.514A. There is big difference in
c value for optimised strucutre.But the same calculation for GGA pseudo
potential gives the lattice parameter values which are good with
experimental values. In literature  previous results for LDA has good
lattice parameter values.
 Which parameter I have to  change in order to get good results for LDA?
  Below is my input and the version i have used is 5.2.1

 &CONTROL
                       title = 'anatase' ,
                 calculation = 'vc-relax' ,
                restart_mode = 'from_scratch' ,
                  pseudo_dir = '/home/suresh/GN2/',
                      outdir
='/home/suresh/Desktop/ashahicheck/asahiopt/tmp/',
                      prefix = 'anatase' ,
                     tstress = .true. ,
                     tprnfor = .true. ,



 /
 &SYSTEM
                       ibrav = 6,
                           A = 3.692,
                           C = 9.471 ,
                         nat = 12,
                        ntyp = 2,
                     ecutwfc = 60 ,
            exxdiv_treatment = 'none' ,



 /
 &ELECTRONS


 /
 &IONS
                  ion_dynamics = 'bfgs' ,

 /
 &CELL
               cell_dynamics = 'bfgs' ,


 /
ATOMIC_SPECIES
   Ti   47.86700  Ti.pz-mt_fhi.UPF
    O   15.99940  O.pz-mt_fhi.UPF
ATOMIC_POSITIONS (crystal)
Ti      0.0000000   0.0000000   0.0000000
Ti      0.5000000   0.0000000   0.7500000
Ti      0.0000000   0.5000000   0.2500000
Ti      0.5000000   0.5000000   0.5000000
O       0.0000000   0.0000000   0.2066000
O       0.5000000   0.0000000   0.5434000
O       0.0000000   0.5000000   0.4566000
O       0.5000000   0.0000000   0.9566000
O       0.0000000   0.5000000   0.0434000
O       0.0000000   0.0000000   0.7934000
O       0.5000000   0.5000000   0.7066000
O       0.5000000   0.5000000   0.2934000
K_POINTS automatic
4 4 2 1 1 1


Thanks in advance.


                  With Regards,
A.Suresh,
Research Scholar,
Madurai Kamaraj University,
Madurai.
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