[CP2K:8997] incorrect number of frequencies in vibrational analysis

[hut... at chem.uzh.ch]

Hi

the MODE_SELECTIVE method should not be used to calculate the
complete vibrational spectrum. The method is best and most
efficient for the calculation of a small number of local
(space or frequency) modes. In your case you probably got
some modes multiple times. There are no negative modes because
you excluded them explicitly.

To get rid (or reduce) possible negative frequencies in the
complete spectrum you have to increase the numerical accuracy.
This might need changing default parameters in all parts of
the calculation. 
- Integral accuracy  -> EPS_DEFAULT
- PW cutoff          -> CUTOFF and REL_CUTOFF
- Geometry optimization -> MAX_FORCE, RMS_FORCE
- SCF convergence    -> EPS_SCF
- Step length in finit difference  -> DX

regards

Juerg 
--------------------------------------------------------------
Juerg Hutter                         Phone : ++41 44 635 4491
Institut für Chemie C                FAX   : ++41 44 635 6838
Universität Zürich                   E-mail: hut... at chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
---------------------------------------------------------------

-----cp... at googlegroups.com wrote: -----To: cp2k <cp... at googlegroups.com>
From: Natalie Schieber 
Sent by: cp... at googlegroups.com
Date: 05/08/2017 08:45PM
Subject: [CP2K:8997] incorrect number of frequencies in vibrational analysis

Dear all,

I am trying to obtain the vibrational frequencies of a periodic system of four benzene molecules. When I run the vibrational analysis with no restriction, I obtain the correct number of frequencies (141), but some of them are negative. However, when I restrict the range of the search, I obtain positive wavenumbers, but more frequencies than should be physically present (152). When I try to run the vibrational analysis with tighter convergence but no range, I get an error.  The relevant part of the input is below. Any help on obtaining 141 positive numbers is appreciated!

&VIBRATIONAL_ANALYSIS
&MODE_SELECTIVE
EPS_MAX_VAL 0.0000000005
EPS_NORM 0.00000002
&END MODE_SELECTIVE
&END VIBRATIONAL_ANALYSIS

Returns an error:  no frequency, range or involved atoms specified  

&VIBRATIONAL_ANALYSIS
&END VIBRATIONAL_ANALYSIS

returns 141 wavenumbers with negatives


&VIBRATIONAL_ANALYSIS
&MODE_SELECTIVE
EPS_MAX_VAL 0.0000000005
EPS_NORM 0.00000002
RANGE 0 50000
&END MODE_SELECTIVE
&END VIBRATIONAL_ANALYSIS

returns 152 positive numbers




Best,
Natalie Schieber




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