CCL:G: Effect of basis set on frequency calculations with g03
- From: "Rajendran Arivazhagan"
- Subject: CCL:G: Effect of basis set on frequency calculations with
- Date: Tue, 17 Oct 2006 23:41:46 -0400
Sent to CCL by: "Rajendran Arivazhagan"
Dear CCL Members,
I am doing frequency calculation for protonated organic molecule using g03.
My molecule have two protonation sites, say for example site1 and site2. Freq
calculation with B3LYP/6-311+G(d) gave an imaginary/negative frequency for site1
and all real frequencies were observed for site2. My input file looks like:
B3LYP/6-311+G(d) SCF=Tight test Opt Freq Pop=full gfprint SCRF=(CPCM,
But the results are completely opposite with B3LYP/3-21G and here negative
frequency was observed for site2 and all real frequencies were observed for
site1. Input file looks like:
B3LYP/3-21G SCF=Tight test Opt Freq Pop=full gfprint SCRF=(CPCM, Solvent=Water)
So which result I can believe and where is the problem? Basis set with
polarization and diffuse functions are not suitable for frequency calculations?
Any suggestion is most welcome. Thank you very much.