"MULTIMODE"; a code to obtain accurate rovibrational energy levels for many-mode molecules

 From: Joel Bowman <bowman - at - euch3g.chem.emory.edu>
 Sender: molecular-dynamics-news-request - at - mailbase.ac.uk
 To: molecular-dynamics-news - at - mailbase.ac.uk
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 Date: Thu, 18 May 2000 11:25:16 -0400 (EDT)
                             Program announcement
 "MULTIMODE"; a code to obtain accurate rovibrational energy levels for
 many-mode molecules by:
 S. Carter,  39, Grove Hill, Caversham, Reading RG4 8PS, UK
 J.M. Bowman,  Department of Chemistry, Emory University, Atlanta GA 30322, USA
 and contributions from N.C. Handy,   Department of Chemistry, Lensfield Road,
 Cambridge CB2 1EW, UK
    "MULTIMODE" is a near-variational procedure for the calculation of
    rovibrational energies of polatomic molecules, adsorbates and clusters.
    The method is based on the Watson normal coordinate hamiltonian for
    non-linear molecules, and proceeds via vibrational SCF and rovibrational
    CI steps.  The complete hamiltonian is used at all times, but approximations
    are made in order to integrate the potential and coriolis terms.  These terms
    are included as N-mode expansions in the normal coordinates, but are
    truncated at the 4-mode terms.  It has been demonstrated that higher terms
    are insignificant compared with the inaccuracies in the potential itself.
    The method has been thoroughly tested for a variety of  triatomic and
    tetraatomic molecules and, in particular, against exact variational results
    for H2CS (6 modes, ref. 1) and more recently it has been applied to
    CH4 (9 modes, ref. 2).  In both cases, excellent convergence
    has been achieved for all of the low-lying vibrational levels.
   "MULTIMODE" can be used in less accurate calculations, for example
 at the SCF
   level alone, or in SCF-CI calculations, where specified numbers of vibrational
   (non-orthogonal) SCF functions are used in a vibrational CI basis.   These
   methods also allow for an adiabatic rotation scheme, which gives reasonable
   values for rotational constants, in particular.
   "MULTIMODE" is currently being extended to include the Watson
   hamiltonian for linear molecules, and also to include the Miller-Adams-Handy
   Reaction Path hamiltonian in order to describe a single large-amplitude
   coordinate, for example the torsion in H2O2.  This will widen the scope of
   molecules that can be handled.
    information:  www.emory.edu/CHEMISTRY/faculty/bowman/multimode
    enquiries:    s.carter - at - reading.ac.uk
    References
    ----------
   1.  S. Carter, J.M. Bowman and N.C.Handy; Theor. Chem. Accts., 100, 191 (1998)
   2.  S. Carter and J.M. Bowman; J. Phys. Chem. 104, 2443 (2000)