Subject: GAMESS: SCF convergence

From: FyD <[email-masked]>
Date: Fri, 25 Oct 2002 12:11:52 +0200 (CEST)

Dear All,

I want to optimize a model to the B3LYP/6-31++G** theory level (TL) using
GAMESS. If I optimize it directly to this TL the first SCF computation does not
converge (with GUESS=HUCKEL). So, to be able to get a B3LYP/6-31++G** optimized
structure, I proceed in two times. I first optimize my model to the 6-31++G** TL
(with GUESS=HUCKEL) and then from the new 6-31++G** optimized Cartesian
coordinates I reoptimized it to the B3LYP/6-31++G** TL (with GUESS=MOREAD) 
providing the 6-31++G** $VEC group. I have the same probleme with a single point
energy determination using the same B3LYP/6-31++G** basis set if I do not
provide a previous $VEC group. 

- However, I am interested in getting B3LYP/6-31++G** energy value using a
SINGLE input and not TWO as I am doing. Is there a way to do this ?

- I do not have this SCF convergence problem if I use MP2 computations for
instance. Is it a known probleme for B3LYP/DFT calculations ?

Thanks, regards, Francois

---

From: Wibke Sudholt <[email-masked]>
Date: Fri, 25 Oct 2002 11:21:57 -0700

Hi,

I observed SCF convergence problems with DFT and diffuse functions in
GAMESS myself. I solved them by

* INTTYP=HONDO and higher than default values for ITOL and ICUT in $CONTRL
  (that means higher integral accuracy)

* FDIFF=.FALSE. in $SCF (that means compute full Fock matrix in each
  iteration)

I hope this helps!

Best regards,

Wibke Sudholt
University of California, San Diego

On Fri, 25 Oct 2002, FyD wrote:

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