Re: CCL:Calculations without Born-Oppenheimer approximation '2nd Call'

Along the lines of Dr Sukumar's response, one can do
 optimizations/frequencies via energy points utilizing BO-based energies
 corrected via the Born-Oppenheimer Diagonal Correction (BODC/DBOC), which
 will at least be one step closer to "non-Born-Oppenheimer"
 geometries/frequencies.
 Psi 3.2 (www.psicode.org) could be made to do this (using a DBOC based on
 SCF or CISD wavefunctions), though currently such an approach could not be
 carried out automatically.
 Steven Wheeler
 --------------------------------------------------------------------
 Steven E. Wheeler                      | phone: 706 542-7379
 Ctr. for Comp. Quantum Chem. | fax:   706 542-0406
 University of Georgia     | e-mail: swheele2|at|ccqc.uga.edu
 Athens, GA  30602-2556      | http://hermes.ccqc.uga.edu
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 > On Tue, 16 Dec 2003 15:11:47 +0100 (MET) Giju Kalathingal wrote:
 >
 >> Last week I had send the following message without
 >> any success. So I am posting it again.
 >>
 >> Dear CCL-all,
 >>
 >> Could you please give me some info on programs
 >> that let me to do quantum chemical calculations
 >> (geometry optimzations and vibrational frequencies)
 >> without Born-Oppenheimer approximation?
 >>
 >> Thanks in advance.
 >>
 >> Giju Kalathingal
 >>
 >> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 >>
 >
 > Perhaps the reason you did not get any response was because your
 > question specifically dealt with programs for geometry optimzations and
 > vibrational frequencies. These concepts (molecular geometry and
 > molecular vibrations) are normally understood within the
 > Born-Oppenheimer approximation. I do not know of any readily available
 > programs that deal with these outside of BO. However quantities such as
 > bond lengths and vibrational frequencies are derivable from experiment
 > and thus these concepts ARE defined beyond the Born-Oppenheimer
 > approximation: equilibrium bond lengths, for instance, would be defined
 > as the peaks in the two-particle radial distribution functions for the
 > two bonded nuclei. See the special issue of Israel Journal of Chemistry,
 > vol.19 (1980) for many papers (and much debate), e.g. those of
 > R.G.Woolley, pp.30-46 and of Carl Trindle, pp.47-53. L. Lathouwers and
 > P. Van Leuven (CPL 52, 439, 1977; PRA 18, 2150, 1978; IJQC S12, 371,
 > 1978) demonstrated that the generator coordinate method could be
 > employed to avoid the BO separation and develop a non-adiabatic
 > formulation of molecular quantum theory.
 >
 > In a series of pioneering papers on hydrides (CPL 3, 705, 1969; PS 185,
 > 90, 1969; PRA 2, 728, 1200, 1675, 1970; PRA 3, 565, 1022, 1971; PRA 4,
 > 457, 1971; PRA 5, 1104, 1972), I.L.Thomas put electrons into electronic
 > orbitals and protons into protonic orbitals (thereby avoiding the BO
 > approximation), antisymmetrized the two kinds of orbitals separately,
 > performed SCF computations and obtained molecular structures and spectra
 > that
 > corresponded to experiment. For instance, the microwave transition
 > frequency of ammonia (conventionally explained by "umbrella
 flipping"
 > between two structures) is now obtained as the transition frequency
 > between protonic orbitals. Subsequently Thomas went on to become
 > vice-president of Occidental Petroleum and did not continue his protonic
 > structure studies. I wrote some programs to do similar computations as
 > part of my candidacy work at Stony Brook in the early 80s, but those are
 > now lost on some magnetic tape somewhere.
 >
 > There are now several computations and programs that go beyond the BO
 > approximation by calculating the nonadiabatic coupling terms or
 > performing a diabatic transformation in multi-reference CI or CASSCF
 > spaces (see e.g. D.R.Yarkony in "Modern Electronic Structure
 Theory"
 > Part I, World
 > Scientific, Singapore, 1995, pp.642-721; W.Domcke, et al. CPL 216,362,
 > 1993; 226, 257, 1994; Neuheuser, Sukumar and Peyerimhoff, Chem.Phys.,
 > 194, 45-64, 1995; Mol.Phys. 95, 61-70, 1998) but none of these can be
 > considered as truly "without Born-Oppenheimer approximation"
 >
 > (PRA=Phys.Rev A; CPL=Chem.Phys.Lett.; IJQC=Int.J.Quantum Chem)
 >
 > N. Sukumar
 > RPI Department of Chemistry
 >
 >
 >
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