[Pw_forum] IR

[Somesh Kumar Bhattacharya]

Hi Shoutian Sun,

With CPMD one can calculate the IR spectra by taking the fourier transform
of the velocity autocorrelation function (VAF). For this, one has to run a
very long simulation ( time scale few picoseconds) and then calculate the
VAF.  You can read a bit about VAF from any standard statistical mechanics
book ( plenty of materials are available online). Also refer to the paper :
J. Phys. Chem. A * 111*, 12810 (2007) regarding the expression for the
fourier transform.

Regarding your problem of tempp changing  at every step, try using the nose
thermostat.

Regards,

Somesh


2009/10/6 shoutian sun <sunshoutian168 at yahoo.com.cn>

> Dear all,
> I want to calculate IR spectrum with cp MD (cp.x) at the temperature of
> 100K(without elec-field).
> And I just make a change the input file of example30 as follows. But in the
> ourput file
> the temperature value: tempp changed every step. Can anyone tell me how can
> I
> calculate IR with cp MD. Thanks in advance.
>
> >&CONTROL
> >  calculation = 'cp',
> >  restart_mode = 'from_scratch',
>  > nstep  = 10000,
> >  iprint = 100,
> >  isave  = 100,
>  > tstress = .FALSE.,
>   >tprnfor = .TRUE.,
> >  tefield = .TRUE.,
> >  prefix = 'mgo',
> >  dt=5.,
> >  pseudo_dir = '/ds13/zfliu/stsun/espresso-4.1/pseudo/',
> >  outdir='/ds13/zfliu/stsun/espresso-4.1/examples/example30/results/tmp'
> >/
> >
> >&SYSTEM
> >  ibrav = 1,
> >  celldm(1) = 15.912,
> >  celldm(2) = 0.0,
> >  celldm(3) = 0.0,
> >  celldm(4) = 0.0,
>  > celldm(5) = 0.0,
>  > celldm(6) = 0.0,
> >  nbnd=128,
> >  nelec=256,
> >  nat  =64,
> >  ntyp =2,
> >  ecutwfc = 40,
> >  ecutrho = 250,
> >  nr1b= 30, nr2b = 30, nr3b = 30,
> >  nspin=1,
> >/
> >
> >&ELECTRONS
> >  emass = 250.d0,
> >  emass_cutoff = 3.d0,
> >  electron_dynamics='damp', ortho_max=30
> >  electron_damping=0.05
> >  startingwfc = 'random',
> >  ampre = 0.02,
> >  efield = 0.0
> >  epol = 3
> >/
> >
> >&IONS
> >  ion_dynamics = 'verlet',
> >  ion_temperature = 'rescaling',
> >  tempw = 100,
> >/
> >
> >&CELL
>  > cell_dynamics = 'none',
> >/
> >
> >ATOMIC_SPECIES
>  >O  1.0 O.pz-rrkjus.UPF
>  >Mg 1.0 Mg.pz-n-vbc.UPF
> >ATOMIC_POSITIONS (bohr)
> >Mg   0.066300000   0.066300000   0.066300000
> >...........
>
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-- 
Somesh Kr. Bhattacharya
Post Doctoral Fellow
Room No. 263,
Leonardo Building,
The Abdus Salam International Centre for Theoretical Physics
Strada Costiera, 11
I-34014 Trieste
Italy
Phone: +39-040-2240399
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