Subject: A BLYP/Becke3LYP frequency problem in G92/DFT

From: <[email-masked]>
Date: Sat, 18 Mar 1995 10:21:31 +1000 (EET)

Hi folks,

I have been using BLYP and Becke3LYP for some large systems where
MP2 frequencies are not feasible here with some success. With one system 
I have a problem. The molecule has D2h symmetry and is like diborane.
Experimentally we know this but are using theory to help the neutron
diffraction studies and to sort out the i.r./Raman bands.

SCF gives reasonable results with two basis sets. BLYP and Becke3LYP
give similar geometries to the SCF but the SCF gives one imaginary
frequency. However the 3 "zero" rotational frequencies are roughly
-30, -20 and -8. The imag freq is -40. I used opt=tight and Int=FineGrid.
The frequency run still shows the forces and predicted displacements
to be good. 

Can anyone sugest what is going on? I will post a summary.

Thanks, Brian.
-- 
NOTE - Change of School name and University address from 1/1/95.
        Associate Professor Brian Salter-Duke (Brian Duke)
School of Mathematical and Physical Sciences, Northern Territory University,
            Darwin, NT 0909, Australia.  Phone 089-466702
e-mail: [email-masked]  or [email-masked]