[CPMD-list] linear response calculation

[Juerg Hutter]

Hi

this needs probably some explanations.

There are three ways you can calculate second derivatives
in CPMD

1) &CPMD
     VIBRATIONAL ANALYSIS FD
   &END
   --> Finite difference calculation
   This should work for all cases, needs the same specifications
   as a normal wavefunction optimization.
   Additional keywords are "FINITE DIFFERENCES" for the step length

2) &CPMD
     VIBRATIONAL ANALYSIS LR
   &END
   --> Linear response calculation
       This method has several known bugs, if you want to use
       it test it for your special type of calculations first.
       Additional input in the &LINRES section

3) &CPMD
     LINEAR RESPONSE
   &END
   &RESP
     PHONON
   &END
   The same method as 2) but different implementation.
   All additional input (like Convergence) through the
   &RESP section.

General: Geometries should be optimized as good as possible,
with lower convergence criteria for both, geometry and wfn.

regards

Juerg

----------------------------------------------------------
Juerg Hutter                   Phone : ++41 1 635 4491
Physical Chemistry Institute   FAX   : ++41 1 635 6838
University of Zurich           E-mail: hutter at pci.unizh.ch
Winterthurerstrasse 190
CH-8057 Zurich, Switzerland
----------------------------------------------------------


On Thu, 3 Feb 2005, Ivaylo Ivanov wrote:

> Hello,
> I'm trying to do vibrational analysis with the option LR (Linear
> Response). The manual says that "A rule of thumb is that good results are
> obtained with a 10 times stricter convergence on the ground state orbitals
> compared to that of the response orbitals." What is not clear to me is how
> to change the convergence criterion for the response orbitals from the
> default value (1.0D-5). Any suggestions would be appreciated. Thanks very
> much in advance.
>
> --Ivaylo Ivanov
>
> --
> Ivaylo Ivanov
> Center for Molecular Modeling | University of Pennsylvania
> 231 S.34 Street,              | Philadelphia,PA 19104-6323
> tel: (215) 573 8697           | fax: (215) 573 6233
> e-mail: iivanov at cmm.chem.upenn.edu
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