Subject: two questions

From: Vlad Cojocaru <[email-masked]>
Date: Mon, 10 Jun 2002 16:24:45 +0200

1. I am using the following input in order to calculate an electron density:

%chk=tap_hf_opt.chk
#P RB3LYP 6-31+G(d) Geom=Checkpoint Cube(40,Density) Guess=Read 
Density=Current

methyl-TAP el.density calculation using optimized (hf 6-31g*) structure

0 1

In the output there is a line that says: "Warning!  SCF SP cutoffs with 
diffuse functions may be unreliable.
 Consider SCF=Tight"
Does anyone have experience with this and is able to explain to me what 
actually it is happening.? Can I simply ignore the warning or should I 
go for SCF=Tight?

2. I have the following input trying to calculate the frequencies of an 
optimized structure at the same level of theory:

%chk=tap.chk
#P Geom=AllCheck Guess=Read RB3LYP/6-31+G(d) FREQ POP=FULL GFPrint

methyl-TAP optimization

0 1

The Gaussian job is broken by this error message:

Not enough memory for a single radius per batch:
 NAngPt=     302 MaxPt=     216.
 Error termination via Lnk1e in /usr/local/g94/l1002.exe.

Can anyone explain to me what is wrong?

Thanks a lot in advance for any kind of advice.
vlad

-- 
Vlad Cojocaru 
Max Planck Institut for Biophysical Chemistry 
Deparment: 060 
Am Fassberg 11, 37077 Goettingen, Germany 
tel: ++49-551-201.1389 
e-mail: [email-masked]

---

From: Jamie Platts <[email-masked]>
Date: Mon, 10 Jun 2002 17:08:52 +0100 (BST)

By default, Gaussian relaxes SCF convergence criteria for single-point
(ie non-optimisation) jobs, to give reasonable energies in less cpu time.
However, this can fall down when diffuse functions are present, since
these might change substantially without affecting the energy much. More
worryingly, the density (and hence any properties), will also be affected
by such changes. I would advise that if you are interested in anything
more than the final SCF energy then always used SCF=Tight.

  As for 2, L1002 solves the CPHF equations for the frequencies, so it
seems your default setting doesn't give you enough memory to run this
particular frequency job. Try increasing with something like:

%Mem=256Mb	! exact figure depends on your machine
%Chk=tap.chk
#P ...

If you can't assign enough memory for your particular molecule, you might
have to use a smaller basis set and/or HF instead of B3LYP for your
freq's. These are usually OK, as you can scale them to (almost) the
correct value. There must be endless discussion of this in the CCL
archives...

  Hope this helps,

  Jamie

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