[Pw_forum] Upper estimation of lattice parameter by LDA pseudopotential -regarding

[Suresh A]

Dear Friends,
                  I optimised anatase structure with LDA pseudopotential.
It upperestimates the lattice parameter values. In literature it is shown
that LDA should underestimate lattice parameters upto 1-2%.

Below is my input and final(optimised) values.
Input lattice parameters.
A =  3.785,
 C =  9.514,

Optimised lattice parameters

A =  3.902,
C =  9.804,

 my input file is as follows.

 &CONTROL
                       title = 'anatase' ,
                      calculation = 'vc-relax' ,
                restart_mode = 'from_scratch' ,
                  pseudo_dir = '/home/suresh/isha/',
                      outdir ='/home/suresh/isha/kriya/',
                      prefix = 'anatase',
                     tstress = .true. ,
                     tprnfor = .true. ,





 /
 &SYSTEM
                       ibrav = 6,
                           A =  3.785,
                           C =  9.514,
                         nat = 12,
                        ntyp = 2,
                     ecutwfc = 110 ,
                     ecutrho = 440





 /
 &ELECTRONS
conv_thr = 1.D-8

 /
 &IONS


 /
 &CELL



 /
ATOMIC_SPECIES
   Ti   47.86700  Ti.pz-n-nc.UPF
    O   15.99940  O.pz-nc.UPF
ATOMIC_POSITIONS (crystal)
Ti       0.000000000   0.000000000   0.000000000
Ti       0.000000000   0.500000000   0.250000000
Ti       0.500000000   0.500000000   0.500000000
Ti       0.500000000   0.000000000   0.750000000
O        0.000000000   0.000000000   0.206600000
O        0.000000000   0.500000000   0.456600000
O        0.500000000   0.000000000   0.543400000
O        0.500000000   0.500000000   0.293400000
O        0.500000000   0.500000000   0.706600000
O        0.500000000   0.000000000   0.956600000
O        0.000000000   0.500000000   0.043400000
O        0.000000000   0.000000000   0.793400000
K_POINTS automatic
4 4 4  0 0 0

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