Ab initio computations of molecular

Carved wooden bears in all shapes and sizes overwhelmed Yngve and me at our visit to Noboribetsu in 1976. There was an afternoon to spare before the opening of the "Oji International Seminar on Theories and Ab Initio Computations of Molecular Electronic Structure" at Tomakomai, Hokkaido in the fall of 1976 so we wished to experience the hot springs. The train left us with a choice of buses, the desdnations of which were clearly indicated in Japanese writing. We found the right one and came to a city in a canyon where the sulfur fumes and hot water let themselves out. The kind reception by Kimio Ohno and Fukashi Sasaki at Hokkaido University remains a vivid memory. 

Bagus, P. S., Liu, B., McLean, A. D., Yoshimine, M. Ab initio computation of molecular structures through configuration interaction. In Computational methods for large molecules and localized states in solids. Herman, F., McLean, A. D., Nesbet, R. K. (eds.). New York Plenum Press 1973, pp. 87-115... 

The ab initio computation of molecular properties - including those associated with time-dependent external electric and magnetic fields - has advanced significantly in the last several decades, yielding accurate models for linear, quadratic, and higher-order response functions. When electron correlation effects play a pivotal... 

S. P. A. Sauer and M. J. Packer, The Ab Initio Calculation of Molecular Properties other than the Potential Energy Surface, Computational Molecular Spectroscopy, P. R. Bunker and P. Jensen, eds., Wiley, London, 2000, Chapter 7, pp. 221. 

CONTENTS Introduction, Thom H. Dunning, Jr. Electronic Structure Theory and Atomistic Computer Simulations of Materials, Richard P. Messmer, General Electric Corporate Research and Development and the University of Pennsylvania. Calculation of the Electronic Structure of Transition Metals in Ionic Crystals, Nicholas W. Winter, Livermore National Laboratory, David K. Temple, University of California, Victor Luana, Universidad de Oviedo and Russell M. Pitzer, The Ohio State University. Ab Initio Studies of Molecular Models of Zeolitic Catalysts, Joachim Sauer, Central Institute of Physical Chemistry, Germany. Ab Inito Methods in Geochemistry and Mineralogy, Anthony C. Hess, Battelle, Pacific Northwest Laboratories and Paul F. McMillan, Arizona State University. 

Here, we report, for the first time, ab initio computations of the six lowest-lying electronic states of Na2" ". These computations utilize the basis set developed to describe the low-lying states of the neutral Nap, molecules (6) and utilize integrals which have been computed previously (, ). The molecular energies computed at the single-configuration self-consistent-field (SC-SCF) level are listed in Table I. These SC-SCF computations should provide relatively reliable potential curves for what are effectively one-electron systems. We do not attempt to describe the electron correlation associated with the core electron motions nor that associated with the polarization of the core electrons by the single valence electron. Thus, while dispersion effects are not well described, the first order ion-induced dipole Interaction and the major electrostatic interactions of the valence electron are probably reasonably well described at the SC-SCF level. Note in Table II, where we list molecular constants for Nap, that the 1 state is bound. Its 1 T. counterpart in the neutral molecule is predicted to be... 

Legrand, J. R, Lajzerowicz, J., Lajzerowicz-Bonneteau, J. and Capiomont, A. (1982). Ferroelastic and ferroelectric phase transition in a molecular crystal tanane. 3.-From ab initio computation of the intermolecular forces to statistical mechanics of the transition. J. Phys., 43, 1117-25. [202]... 

The introduction of Valence Bond theory has motivated the search for structural regularities that can be interpreted by models of local electronic features, such as the powerful model of Valence Shell Electron Pair Repulsion [93,94] theory. Alternative approaches, based on Molecular Orbital theory, have led to the discovery of important rules, such as the Woodward-Hoffmann orbital symmetry rules [95] and the frontier orbital approach of Fukui [96,97], As a result of these advances and the spectacular successes of ab initio computations on molecular... 

Whereas the concepts and method described in this contribution are equally applicable to various approximate and more advanced quantum-chemical representations, the basic concepts will be discussed and illustrated within the framework of the conventional Hartree-Fock-Roothaan-Hall SCF LCAO ab initio representation of molecular wave functions and electronic densities, as can be computed, for example, using the Gaussian family of computer programs of Pople and co-workers. The essence of the shape analysis methods will be discussed with respect to some fixed nuclear arrangement K note, however, that the generalizations will involve changes in the nuclear arrangement K. 

AB Initio Computation of Unusual Time-Dependent Molecular Processes Using Judiciously Chosen Expansions for the rlrCtj... 

AB INITIO COMPUTATION OF UNUSUAL TIME-DEPENDENT MOLECULAR PROCESSES USING JUDICIOUSLY CHOSEN EXPANSIONS FOR THE vpftj... 

Calculations based on ab initio methods of molecular electronic structure theory are very demanding computationally and any review of progress over the past two decades must be made against the background of the continually increasing power of contemporary computers. The past 20 years have witnessed a relentless increase in the power of computing machines. It has been observed that the processing power of computers seems to double every 18 months. As the historian Roberts [100] points out in his book Twentieth Century... 

Sauer, S. P. A., Packer, M. J. (2000). The Ab initio calculation of molecular properties other than the potential energy surface. In P. R. Bunker P Jensen (Eds.), Computational molecular spectroscopy (pp. 221-252). London Wiley. 

The last twenty years have seen remarkable advances in molecular quantum mechanics. The traditional methods expounded in the first edition of this book have been implemented on a grand scale, and the ab initio calculation of molecular electronic structure and properties, using freely available programs and increasingly powerful computers, has become commonplace. Indeed computational chemistry now has its own books and journals and plays a respected role in the study of molecular processes of all kinds— whether in interstellar space or in the chemical laboratory or in biological systems. 

The variational methods of the configuration interaction (Cl) type and the perturbative-type methods relying on the exponential coupled-cluster (CC) Ansatz are the most often used approaches in ab initio computations of highly accurate molecular properties, in particular of the potential energy surfaces (PESs) or curves (PECs) for the purposes of molecular dynamics [for recent reviews, see Refs. (1-4)]. In this latter case it is essential that the entire surface — or its various one- or multi-dimensional cuts — is available for a wide enough range of molecular geometries. 

Figure 4.50 from Molecular Parameters for Organosilicon Compounds Calculated from Ab Initio Computations, Grigoras S and T H Lame, Journal of Computational Chemistry 9 25-39, 1988. Reprinted by permission of John Wiley Sons, Inc. 

The quantum mechanics methods in HyperChem differ in how they approximate the Schrodinger equation and how they compute potential energy. The ab initio method expands molecular orbitals into a linear combination of atomic orbitals (LCAO) and does not introduce any further approximation. 

Computer simulations therefore have several inter-related objectives. In the long term one would hope that molecular level simulations of structure and bonding in liquid crystal systems would become sufficiently predictive so as to remove the need for costly and time-consuming synthesis of many compounds in order to optimise certain properties. In this way, predictive simulations would become a routine tool in the design of new materials. Predictive, in this sense, refers to calculations without reference to experimental results. Such calculations are said to be from first principles or ab initio. As a step toward this goal, simulations of properties at the molecular level can be used to parametrise interaction potentials for use in the study of phase behaviour and condensed phase properties such as elastic constants, viscosities, molecular diffusion and reorientational motion with maximum specificity to real systems. Another role of ab initio computer simulation lies in its interaction... 

Equation (2) was also used to calculate quantum chemical approach. On the basis of previous results [19], calculated electrostatic potentials were computed from ab initio wave functions obtained in the framework of the HF/SCF method using a split-valence basis set (3-21G) and a split-valence basis set plus polarisation functions on atoms other than hydrogen (6-31G ). The GAUSSIAN 90 software package [20] was used. Since ab initio calculations of the molecular wave function for the whole... 

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