Computation ab initio

Figure 4. Spin-orbit splitting in AT — 1 and 2 vibronic levels of the state of NCN. Solid lines connect the results of calculations thar employ ab initio computed potential curves [28], For comparison the results obtained by employing experimentally derived potential curves (dashed lines) [30,31] are also given. Full points represent energy differences between P — K — and P — K spin levels, and crosses are differences between P — K + I and P — K levels.

Figure 8. Three-dimensional mean-potential surface for the X IT state of HCCS, (Pi, Pa, y), presented in form of its ID sections. Curves represent the function given by Eq. (75). (with Ati — 0.0414, k2 — 0.952, tt 2 — 0.0184) for fixed values of coordinates p, and P2 (attached at each curve) and variable y — 4 2 4t Here y — 0 corresponds to cis-planar geometry and Y = ft to trans-planar geometry. Symbols results of explicit ab initio computations.

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. 

Model Builder to get a reasonable starting geometry, with the possibility of refining the geometry by semi-empirical calculations before submitting it to ab initio computation. 

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... 

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. 

It should be noted that in the spirit of the global simulation, all the interaction potentials used are obtained from ab initio computations, although at the present time only at the SCF level with minimum basis sets. 

It can be seen from Figures 3.7 and 3.8 that the calculations reproduce very well not only the experimental spectra but also the experimentally observed isotopic shifts indicating a high reliability of the computational method. According to this comparison, definite attribution can be made for even the difficult Raman bands that cannot be assigned based solely on the experimental results. It is, however, necessary to mention at this point that the calculated Raman spectrum provided directly by the ab initio computations correspond to the normal Raman spectrum with the band intensity determined by the polarizability of the correlating vibration. Since the intensity pattern exhibited by the experimentally recorded resonance Raman spectrum is due to the resonance enhancement effect of a particular chromophore, with no consideration of this effect, the calculated intensity pattern may, in many... 

Yang, W., 1992, Electron Density as the Basic Variable A Divide-and-Conquer Approach to the Ab Initio Computation of Large Molecules , J. Mol. Struct. (Theochem), 255, 461. 

Clementi, E. (1965) Tables of atomic functions, in Supplement to the paper Ab initio computations in atoms and molecules , IBMJ. Res. Develop., 9, 2-19. 

DESIGN OF NEXT GENERATION FORCE FIELDS FROM AB INITIO COMPUTATIONS BEYOND POINT CHARGES ELECTROSTATICS... 

SIBFA [2, 13] is a polarizable molecular mechanics procedure, formulated as a sum of five energy contributions, each of which is destinated to reproduce its counterpart from reference EDA ab initio computations. The intermolecular interaction energy is formulated as ... 

As for the charge-charge term, x is a constant depending on the chosen level of reference ab initio computation and converges to the classical form as r increases. 

Piquemal J-P (2004) Evaluation of molecular interactions in bioinorganic systems from ab initio computations to polarizable force fields. PhD Thesis, UPMC number 2004PA066267, Universite Pierre et Marie Curie, Paris, France... 

Gresh N, Piquemal J-P, Krauss M (2005) Representation of Zn(II) complexes in polarizable molecular mechanics. Further refinements of the electrostatic and short-range contribution of the intermolecular interaction energy. Comparisons with parallel ab initio computations. J Comput Chem 26 1113... 

Clementi, E., F. Cavallone, and R. Scordamaglia. 1977. Analytic Potentials from ab Initio Computations for the Interaction Between Biomolecules. 1. Water with Amino Acids. J. Am. Chem. Soc. 99, 5531-5545. 

Ragazzi, M., D. R. Ferro, and E. Clementi. 1979. Analytical Potentials from Ab Initio Computations for the Interaction Between Biomolecules. V. Formyl-triglycyl Amide and Water. J. Chem. Phys. 70, 1040-1050. 

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