From chemistry-request@ccl.net Thu Jun 25 14:30:55 1992
Date: Thu, 25 Jun 92 13:04:49 -0400
From: bbesler@ouchem.chem.oakland.EDU (Brent H. Besler)
Subject: problems with Mopac ESP charges with anions
To: chemistry@ccl.net
Status: RO

A number of months ago, I remember a discussion of problems with anions
having ESP charges calculated using Mopac 6.0.  Please send email to 
bbesler@ouchem.chem.oakland.edu if you have such problems as I want to 
work on fixing them.

From chemistry-request@ccl.net Thu Jun 25 14:41:36 1992
Date: Thu, 25 Jun 1992 11:45 CST
From: MCCCM@royal.crc.uno.EDU
Subject: help
To: chemistry@ccl.net
Status: RO

Dear Folks,

I am an earlier Gaussian programms, I carried out at the ab initio hf/3-21g
Level. It has 210 Basis Function. And I had gotten an error like that:
Erroneous write. write -1 instead of 4096
File system characteristics:
  Fragment size =0
  Total blocks  =4002240
  Free blocks   =2744299
  Job blocks max=204800
File characteristics:
  File descriptor=7
  Words to extend=27136
 out2e will use a cutoff of  1.00E-10
 Standard cutoffs selected in Shell.
 error termination in lnk1e.


And my input file was :

# USER=concha
# QSUB -r big
# QSUB -s /bin/sh
# QSUB -lm 4Mw
# QSUB -lM 4Mw
# QSUB -lt 25300
# QSUB -lT 25400
# QSUB -q standby
#
ja
set -x
cd $TMP
cfs get check.chk
date
#
cat > big.dat << EOF
%chk=big.chk
#N HF/3-21G OPT NAME=MONICA

big

0,1
Z-MATRIX.......

Any help you can provide will be greatly appreciated.
Please send responses directly to me.

Monica Concha
Dept. of Chemistry
University of New Orleans
New Orleans LA 70148
Email: Bitnet%"mcccm@uno"

From chemistry-request@ccl.net Thu Jun 25 15:24:14 1992
Date: Thu, 25 Jun 92 14:29:28 -0400
From: jle@world.std.COM (Joe M Leonard)
Subject: Sybyl FF VdW Term
To: chemistry@ccl.net
Status: RO

I've been looking over the J Comp Chem article regarding the
Sybyl 5.2 force field, and I'm curious as to the functional form
of the VdW term.  The paper lists:

        E = k(ij) * (1/a**12 - 2/a**6)

where

        a = r(ij) / (R(i) + R(j))

with R being the defined VdW radius.  This term raises the energy (is
repulsive) when r(ij) < (R(i) + R(j)), but lowers the energy when
the reverse is true.  Is this the correct behavior, in that the force
field is parameterized assuming such longer-distance E-lowering?

This seems odd, as increasing the number of atoms in a structure
serves to lower the E?  Would it not be more reasonable to have the
VdW term drop to zero rather than such negative numbers?

I'm not at all familiar with the Sybyl Force Field, and would appreciate
any comments from those who are - or from Tripos directly...

Thanks in advance,

Joe Leonard
jle@world.std.com


From chemistry-request@ccl.net Thu Jun 25 16:24:21 1992
Date: Thu, 25 Jun 92 14:53:20 -0400
From: jle@world.std.COM (Joe M Leonard)
Subject: Sybyl FF followon
To: chemistry@ccl.net
Status: RO

Before I get flamed for forgetting the underlying physics...

Granted, the VdW term "covers" dispersion forces (which makes
neg E terms ok), but...

1) Is the force field able to "accurately" treat these - i.e. is the
   VdW cutoff a computational or a methodological requirement?

2) What is a reasonable cutoff - the paper lists 8 A, but should
   this be lower/higher?

3) Has the FF changed/evolved since the paper?

*sigh* I guess I should check deeper into the library before posting...

Joe Leonard
jle@world.std.com

P.S. The asbestos undies still fit... :-)


From chemistry-request@ccl.net Thu Jun 25 16:38:13 1992
Date: Thu, 25 Jun 92 06:47 CDT
From: CUNDARIT%MEMSTVX1.BITNET@OHSTVMA.ACS.OHIO-STATE.EDU
Subject: Lu and Sc calcs.?
To: chemistry@ccl.net
Status: RO

Fellow Net-minders,

        Since I'm away from Memphis for the summer and don't have ready
access to a chemistry library, I was wondering if anybody had seen or heard
of the following paper.  I saw it referenced in the book "Selective Hydrocarbon
Activation" edited by Julian A. Davies et al., in a chapter by Patricia
L. Watson (DuPont, Central Research).
        The partial reference is PL Watson, W Fultz, MS Thompson, N Rosch
and V Jahns, Organometallics - in press.  I keep a close eye on Organometallics
but may have missed it.  From what I gather the paper deals with INDO
calculations on Cp2Lu-Ph and its Sc analogue, and seems relevant to our ab-
initio work.  If anybody has seen, or heard, of this paper (an address or phone
no. of the authors would probably be the best shot) and could give a completed
or revised reference, I would appreciate it greatly.

                                        Thomas R. Cundari
                                        Assistant Professor
                                        Department of Chemistry
                                        Memphis State University
                                        Memphis, TN 38152
                                        phone:301-251-2272(summer)
                                        fax:301-251-2255(summer)
                                        e-mail:cundarit@memstvx1.memst.edu

From chemistry-request@ccl.net Thu Jun 25 18:26:23 1992
Date: Thu, 25 Jun 1992 16:45:38 -0400
From: dam@retina.chem.psu.EDU (K.V. Damodaran)
Subject: Sybyl FF followon
To: chemistry@ccl.net
Status: RO

This is in response to a posting "Sybyl FF followon"
>2) What is a reasonable cutoff - the paper lists 8 A, but should
   this be lower/higher?
I guess One has to fix the cutoff depending on the density of the
system. In a low density system with 8A cutoff, a molecule may just
see the nearest neighbours only.

dam@retina.chem.psu.edu