Journal ArticleDOI
Calculation of ground and excited state potential surfaces of conjugated molecules. I. Formulation and parametrization
A. Warshel,Martin Karplus +1 more
TLDR
In this article, Levitt and Levitt developed a method for the consistent calculation of ground and excited state potential surfaces of conjugated molecules, which is based on the formal separation of u and 7r electrons, the former being represented by an empirical potential function and the latter by a semi-empirical model of the Pariser-Parr-Pople type corrected for nearest-neighbor orbital overlap.Abstract:
A formulation is developed for the consistent calculation of ground and excited state potential surfaces of conjugated molecules. The method is based on the formal separation of u and 7r electrons, the former being represented by an empirical potential function and the latter by a semiempirical model of the Pariser-Parr-Pople type corrected for nearest-neighbor orbital overlap. A single parameter set is used to represent all of the molecular properties considered; these include atomization energies, electronic excitation energies, ionization potentials, and the equilibrium geometries and vibrational frequencies of the ground and excited electronic states, and take account of all bond length and bond angle variations. To permit rapid determination of the potential surfaces, the u potential function and SCF-MO-CI energy of the r electrons are expressed as analytic functions of the molecular coordinates from which the first and second derivatives can be obtained. Illustrative applications to 1,3butadiene, 1,3,5-hexatriene, a,w-diphenyloctatetraene, and 1,3-cyclohexadiene are given. detailed interpretation of electronic transitions and A concomitant photochemical processes in conjugated molecules requires a knowledge of the ground and excited state potential surfaces. The determination of such surfaces has long been a goal of theoretical chemistry. Difficulties in a reliable a priori approach to the problem for a system as simple as ethylene2 are such that calculations for more complicated molecules are prohibitive at present. Consequently, a variety of methods that utilize experimental data have been introduced. Completely empirical treatments, in which the energy surface is expressed as a function of potential parameters fitted to the available information (1) Supported in part by Grant EY00062 from the National Institute of Health. (2) U. Kaldor and I. Shavitt, J . Chem. Phys., 48, 191 (1968); R. J. Buenker, S. D. Peyerimhoff, and W. E. Kammer, ibid., 55, 814 (1971). (equilibrium geometry, vibrational frequencies, etc.), have had considerable success in applications to molecules for which a localized electron description is app l i~ab le .~ The great advantage of this type of approach, which leaves open questions of reliability when extended from one class of molecules to another, is the ease and speed of the calculations; this had made possible applications to systems as large as certain nucleic acids and globular proteins. For conjugated molecules, however, the importance of delocalization introduces difficulties into such an empirical treatmenL5 (3) (a) See, for example, J. E. Williams, P. J . Stand, and P. v. R. Schleyer, Annu. Reu. Phys. Chem., 19, 531 (1969); (b) S. Lifson and A. Warshel, J . Chem. Phys., 49, 5116 (1968); A. Warshel and S . Lifson, ibid., 53, 8582 (1970). (4) M. Levitt and S. Lifson, J. Mol. B i d , 46, 269 (1969); M. Levitt, Nature (London), 224, 759 (1969). ( 5 ) C. Tric, J . Chem. Phys., 5 1 , 4778 (1969). Journal of the American Chemical Society 1 94:16 1 August 9, 1972read more
Citations
More filters
Journal ArticleDOI
Structural predictions for the c116 molecule
TL;DR: In this article, a combination of topological and quantum mechanical techniques is used to predict the energetically favored isomer set for the experimentally detected but as yet uncharacterized C116 fullerene.
Journal ArticleDOI
Inversion potentials in the ground and excited electronic states of 9,10‐dihydroanthracene as probed by the absorption and fluorescence spectra of jet‐cooled molecules
TL;DR: In this paper, the inversion potentials in the ground and the lowest excited singlet states of 9,10−dihydroanthracene were deduced from the fit of the absorption and fluorescence spectra of jet-cooled molecules to model potentials.
Journal ArticleDOI
A study of excited state molecular vibrations of aromatic hydrocarbons
TL;DR: Vibrational frequencies in excited and ionized states are calculated for primary aromatic hydrocarbons, on the basis of MO calculations of transition energies and normal coordinate calculations for ground state molecules as discussed by the authors.
Journal ArticleDOI
Time-dependent density functional methods for Raman spectra in open-shell systems.
Fredy W. Aquino,George C. Schatz +1 more
TL;DR: An implementation of a time-dependent density functional theory (TD-DFT) linear response module in NWChem is presented and it is applied to the calculation of resonant Raman spectra in open-shell molecular systems using the short-time approximation.
Journal ArticleDOI
Nonvalence Correlation-Bound Anion States of Spherical Fullerenes
TL;DR: A one-electron model Hamiltonian is presented for characterizing nonvalence correlation-bound anion states of fullerene molecules, which are the finite system analogs of image potential states of metallic surfaces.