[CPMD-list] Fd and LR in vibrational analysis

[Juerg Hutter]

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
>> 
>