[Pw_forum] benzoic acid structure optimization

[mohnish pandey]

30 Rydberg at least for wavefunction cutoff and 240 for charge density.

On Wed, May 2, 2012 at 9:03 AM, matt reish <reishme04 at gmail.com> wrote:
> Thanks for the reply, seemed to be going way too fast for what I had read I
> that I should expect. Any thoughts on what would be more reasonable cutoffs
> for wavefunction and density? Would it be reasonable to try to attain a
> useable result on a "cluster" using 8 processors?
>
> Cheers,
>
> Matt
>
>
> On Wed, May 2, 2012 at 3:02 PM, Axel Kohlmeyer <akohlmey at gmail.com> wrote:
>>
>> 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
>> >
>> > _______________________________________________
>> > Pw_forum mailing list
>> > Pw_forum at pwscf.org
>> > http://www.democritos.it/mailman/listinfo/pw_forum
>> >
>>
>>
>>
>> --
>> Dr. Axel Kohlmeyer
>> akohlmey at gmail.com  http://goo.gl/1wk0
>>
>> College of Science and Technology
>> Temple University, Philadelphia PA, USA.
>
>
>
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-- 
Regards,
MOHNISH,
-----------------------------------------------------------------
Mohnish Pandey
BTech-Mtech, IIT Kanpur
Senior Project Associate,
Department of Chemical Engineering,
IIT KANPUR, UP, INDIA
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