Subject: CCL:Large Mass Atoms

From: "Jens Spanget-Larsen" <[email-masked]>
Date: Thu, 14 Jun 2001 10:38:04 +0100

[email-masked]:

> I was wondering if anyone can help me out with an isotope problem
> in G98.  I want to set the value of some of my atoms to a very 
> large mass, but I'm not sure how the input file should look.  Do I 
> need two seperate jobs to do this?  Any help will be greatful.  

Dear Benjamin,

in order to specify nuclear masses different from the atomic default 
values, you need to activate the option 'readiso' to the 'freq' 
keyword. Additional input is then required, placed after the 
definition of molecular coordinates in the input stream.  The 
additional input consists of: First one line with two numbers: 
temperature (in K) and a scaling factor (say, unity).  Then one line 
per atom, with specification of the nuclear mass (amu) to be applied 
in the calculation of molecular vibrations ('freq'). 

In the sample input below, the molecular geometry is read from the 
chk-file ('geom=check'), and also the force constant matrix is read 
> from this file ('readfc' option to the 'freq' keyword). Hence, the 
job assumes that a previous run has stored the appropriate date from 
'opt' and 'freq' calculations in the chk-file. The job specified 
below only takes a second or two, since the force constant matrix 
need not to be recalculated. - In this example, the nuclear masses 
are entered as whole numbers (for simplicity); Gaussian then selects 
the appropriate values for the isotopes in question. If you don't input 
whole number values, Gaussian adopts the value entered "as is".

Good Luck, Jens >--<

------------------------------------------------
%chk=PhO_VTZ
#t B3LYP/cc-pVTZ Freq(ReadFC,ReadISO) Geom=Check

O(18) Phenoxyl Radical

  0  2

298.150  1.00000
12
12
12
12
12
12
18
1
1
1
1
1

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
JENS SPANGET-LARSEN         Phone: +45 4674 2000 (RUC)
Department of Chemistry            +45 4674 2710 (direct)
Roskilde University (RUC)   Fax:   +45 4674 3011 
P.O.Box 260                 E-Mail: [email-masked]
DK-4000 Roskilde, Denmark   http://virgil.ruc.dk/~jsl/
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=