[CPMD-list] Fd and LR in vibrational analysis

[Yong Zhang]

I am a little confused.
In vibrational analysis, FD is used for first derivative, then how is the
second derivative calculated for a job "VIBRATIONAL ANALYSIS FD" ? FD or LR?

Best wishes,


On 11/28/06, Juerg Hutter <hutter at pci.unizh.ch> wrote:
>
> Hi
> > Thanks for the reply. I found the paper, which discussed the LR method.
> > For the FD method in CPMD, I guess the first order derivative is
> calculated
> > from finite difference method as indicated in the output file. Is the
> second
> > order derivative calculated from those first order derivative simply
> using
> > finite difference method one more time? If not, how is the second order
> > derivative calculated?
> > Thanks a lot
> >
>
> You are one off. All first derivatives in CPMD are calculated using
> analytic formulas. Linear Response (LR) is needed to calculate
> second order derivatives (e.g. dynamical matrix). The finite
> difference (FD) method therefore is used on gradients (=first
> derivatives) of the energy in the vibrational analysis.
>
> regards
>
> Juerg Hutter
>
>
>
> > Yong
> >
> >
> > On 11/23/06, Juerg Hutter <hutter at pci.unizh.ch> wrote:
> >>
> >> Hi
> >>
> >> >
> >> > I am just wondering where I can get detailed description of the FD
> and
> >> LR
> >> > methods used for vibrational analysis in CPMD, for example, the
> original
> >> > references. Thanks a lot.
> >> >
> >>
> >> See Reference 94 in the manual
> >>
> >> \bibitem{apdsmp} A. Putrino, D. Sebastiani and M. Parrinello,
> >> J. Chem. Phys. {\bf 113}, 7102 (2000)
> >>
> >>
> >> regards
> >>
> >> Juerg Hutter
> >>
> >
>
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