Force fields anharmonic molecular

Brooks, R. Bruccoleri, B. Olafson, D. States, S. Swami-nathan, and M. Karplus, J. Comput. Chem., 1983, 4, 187-217. 

Van Gunsteren and H. J. C. Berendsen, BIIOMOS, Laboratory of Physical Chemistry, ETH, Zurich, 1996. 

a program for molecular dynamics developed in the laboratory of J. Hermans, Department of Biochemistry, University of North Carolina, Chapel Hill. 

Levitt, M. Hirshberg, R. Sharon, and V. Daggett, Comput. Phys. Commun., 1995, 91, 215-231. 

Molecular Dynamics Program under development at the University of Illinois under the direction of K. Schulten. 

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A major difficulty in the experimental determination of anharmonic force fields is the burgeoning number of force constants at higher-orders (Table 4, vide infra) compared with the extent of accessible data. As a consequence, reliable experimental anharmonic force fields are available for only a small number of simple molecules. Within the last decade, determination of harmonic and anharmonic molecular force fields by methods of molecular electronic structure theory has become one of the most successful applications of computational quantum chemistry. In Table 1 those species are indicated (without references given to the original publications) for which full force fields have been determined, at least at the HE level of theory and at least up to quartic force constants. 

The procedure and pertinent issues one has to consider when determining anharmonic force fields by methods of electronic structure theory may be described as follows. Once the definition of molecular force constants involving selection of an appropriate coordinate system is clear, one may need to identify all unique force (potential) constants to be determined. Then selection of the reference geometry follows, which affects precision of the force field determined and how the theoretical force field can be transformed from one coordinate system (representation) to another. Given that an appropriate basis set and level of electronic structure theory are chosen for the actual computations, the necessary quantum chemical calculations can be performed after one has carefully considered how to obtain the high-order force constants from low-order analytic information without much loss of precision. Last but not least one needs to understand the potential uses and misuses of anharmonic molecular force fields. 

ACES II Anharmonic Molecular Force Fields Bench-mark Studies on Small Molecules Complete Active Space Self-consistent Field (CASSCF) Second-order Perturbation Theory (CASPT2) Configuration Interaction Core-Valence Correlation Effects Coupled-cluster Theory Density Functional Theory (DFT), Hartree-Fock (HF), and the Self-consistent Field G2 Theory Heats of Formation Hybrid Methods Hydrogen Bonding 1 M0ller-Plesset Perturbation Theory NMR Data Correlation with Chemical Structure Photochemistry Proton Affinities r 2 Dependent Wave-functions Rates of Chemical Reactions Reaction Path Following Reaction Path Hamiltonian and its Use for Investigating Reaction Mechanisms Spectroscopy Computational... 

For instance, the quantum chemical literature is full of comparisons between computed harmonic frequencies and observed fundamental ones. While this may be acceptable in situations where an anharmonic force field calculation (see Anharmonic Molecular Force Fields) is technically impossible, the anharmonicity a>i — v, of a fundamental may easily range from 2 to 200 cm- and therefore such a comparison is essentially meaningless for benchmark quality results. Yet for polyatomics, the experimentally derived harmonic frequencies are often associated with large uncertainties (cf. the C2H4 example at the end of this article) due to indeterminacies, and often the only meaningful comparison will be between computed and observed fundamentals, requiring the ab initio calculation of the anharmonic part of the force field. 

Anharmonic Molecular Force Fields Basis Sets Correlation Consistent Sets Complete Active Space Self-consistent... 

AMBER A Program for Simulation of Biological and Organic Molecules Anharmonic Molecular Force Fields ... 

Biological and Organic Molecules Anharmonic Molecular Force Fields Carbocation Force Fields Carbohydrate Force Fields CHARMM The Energy Function and Its Parameterization Force Fields A Brief Introduction Force Fields A General Discussion Force Fields CFF Force Fields MM3 GROMOS Force Field and OPLS Force Fields). The multitudinous issues related to achieving convergence will be discussed below. 

Anharmonic Molecular Force Fields 1 13 CTIS, 21 rue de la BannUre, 69003 Lyon, France... 

Applications of ab initio quantum mechanical methods are described in ECC articles by Charles Bauschlicher Transition Metals Applications), Weston Borden Diradicals), Attila Csaszar Anharmonic Molecular Force Fields), Michael Dolg Lanthanides and Actinides), and Jan Martin Benchmark Studies on Small Molecules). 

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