Subject: Gaussian98: SCF convergence failure. Tips?

From: "Fernando De La Vega" <[email-masked]>
Date: Sat, 04 May 2002 14:54:59 -0700

Dear all,
  I have been trying to optimize the geometry of the cations of some organic 
polycenes analogs containing nitrogens using DFT. While the neutral 
structures converge with no problems, the cations fail to converge. The 
first iteration simply stalls in the SCF part that does not achieve 
convergence. I have tried every combination of keywords I can think of with 
no success. I have preoptimized the geometries using AM1 with the same 
results. There are no metal centers or anything exotic here, so why the 
problems? Looking through the archives I find that part of the problem seem 
to be the initial guess generated by Gaussian98 which is not very good 
quality (why they don't improve this before adding new features is something 
I cannot understand -at the end, what good is a package that can calculate 
almost anything you can think of but fails in generating the initial 
structure?-). Anyway, I was wondering if you fellows have any strategies or 
suggestions. I will as usual summarize. Thanks.

Typical command line I have been using:

#P ROB3LYP/6-31G(d,p) Opt SCF=(MAXCYCLE=300,NoVarAcc,Tight) POP=FULL
Density=Current GFInput Integral(Grid=Ultrafine) IOP(6/7=3) 6D 10F

... and variations thereof. I am using G98 revision 7 and also 11.

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