[Pw_forum] benzoic acid structure optimization

[matt reish]

Hi PW list,

I am working with Quantum Espresso (v4.3.2.1) in the hopes of attaining
Raman phonon frequencies of a benzoic acid crystal. I attained the
optimized output geometry from a CASTEP calculation in the supplemental
material of a paper. This geometry was used by the authors to calculate
accurate IR phonon frequencies. I used a 'relax' calculation in Quantum
Espresso on the optimized geometry but this led to large shifts in the
atomic positions in the lattice and unreasonable structures for the
molecules in the lattice after finding the optimized structure. My question
is does anyone have a some experience calculating organic crystals in
Quantum Espresso that could give me some tips?

Here is my input file minus the atomic posititions:

&CONTROL
                       title = 'benzacidscftest' ,
                 calculation = 'relax' ,
                restart_mode = 'from_scratch' ,
                      outdir = '/home/mreish/tmp/' ,
                  pseudo_dir = '/usr/share/espresso/pseudo/' ,
                      prefix = 'batest5' ,
                     disk_io = 'default' ,
                       nstep = 600 ,
 /
 &SYSTEM
                       ibrav = 12,
                           A = 5.4996 ,
                           B = 5.1283 ,
                           C = 21.950 ,
                       cosAB = 0 ,
                       cosAC = -.128276341 ,
                       cosBC = 0 ,
                         nat = 60,
                        ntyp = 3,
                     ecutwfc = 5 ,
                     ecutrho = 40 ,
 /
 &ELECTRONS
            electron_maxstep = 200,
                    conv_thr = 1.0d-11 ,
 /
 &IONS
 /
ATOMIC_SPECIES
    C   12.01000  C.pbe-rrkjus.UPF
    O   16.00000  O.pbe-rrkjus.UPF
    H    1.00000  H.pbe-rrkjus.UPF
ATOMIC_POSITIONS angstrom

K_POINTS automatic
  1 1 1   1 1 1


Cheers,

Matthew Reish
University of Otago
Dunedin
New Zealand
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