RE: Freezing atoms-modredundant

You could use Molden to freeze atoms in the zmatrix. I have found writing a
 cartesian file with Mopac, then put zero for optimisation flags that you want to
 freeze. Then use Mopac to do a single point calculation, and include AIGOUT
 keyword and you get an equivalent zmatrix usable in Gaussian. Its not perfect
 but I have found it useful.
 I wonder also if you need some zeros after immediately after the atom labels,
 should it be ?
 C 0 0.000 0.000 0.000
 C 0 0.000 1.500 0.000
 James, Bath.
 -----Original Message-----
 From: Computational Chemistry List [mailto:chemistry-request)at(ccl.net]On
 Behalf Of Aaron Deskins
 Sent: 04 June 2003 15:01
 To: chemistry)at(ccl.net
 Subject: CCL:Freezing atoms-modredundant
 Hello all,
    I have (hopefully) a relatively simple question. I'm trying some
 simple test calculations using Gaussian 98, but am running into a little
 problem freezing atom positions. Essentially I want to freeze a few
 atoms, and allow others to relax. Below is a test file. The problem I
 see is that the geometry optimization algorithm moves all atoms to the
 same location on first pass and subsequently causes the program to
 crash. I've tried different atoms and arrangements with no luck. Any
 suggestions?  Thank you
 # opt(maxcycle=200,modredundant) hf/lanl2dz scf(diis,maxcycle=300)
 Title Card Required
 0  3
 c 0.0000000000 0.0000000000 0.0000000000
 c 2.7718585823 0.0000000000 0.0000000000
 c 0.0000000000 2.7718585823 0.0000000000
 c 2.7718585823 2.7718585823 0.0000000000
 1 f
 2 f
 3 f
 --
 Aaron Deskins
 Graduate Student
 Chemical Engineering
 Purdue University
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