[Pw_forum] benzoic acid structure optimization

[Axel Kohlmeyer]

On Tue, May 1, 2012 at 10:53 PM, matt reish <reishme04 at gmail.com> wrote:
> 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?


matt,

you are using a *ridiculously* low wavefunction
and density cutoff, that means your basis set
is *far* too small. unphysical results are the
logical consequence.

axel.


>
> 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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-- 
Dr. Axel Kohlmeyer
akohlmey at gmail.com  http://goo.gl/1wk0

College of Science and Technology
Temple University, Philadelphia PA, USA.