STOs force fields

Experimental results indicate that for the cis isomer of 1,2-di-ter/-butylcyclohexane (8a), either the chair (84) or the boat (85) conformation is the most stable, whereas for the trans isomer (8b) the diaxial chair and the twist (86) or boat (87) forms are supposed to be in equilibrium. According to MM calculations of the ds isomer, a boat form is preferred when Bartell s force field (36) is used, whereas with Lifson s force field (30) the chair form is predicted (87). Schafer performed ab initio calculations with the STO-3G, basis set on the final structures resulting from these MM calculations and found the boat conformer to be consistently more stable than the chair (87). For the trans isomer (8b), MM calculations again are inconsistent, but ab initio calculations on the final MM geometries result in almost... 

Single determinant ab initio MO with STO-3G minimal basis set. The force field used is Bartell s older version (186). 

An X-ray analysis 34a) of ( ),( ),( )-l,5,9-cyclododecatriene (38) suggested that this molecule is most comfortable in a twisted chiral conformation of D3 symmetry, and a dynamic NMR study and a force-field calculation Mb) estimated AG = 8.6 kcal/mol for the racemization process between two enantiomeric D3 conformers. A pseudochair conformation of similar D3 symmetry was also suggested35) for 1,5,9-cyclodo-decatriyne (39), following an ab initio STO-3G calculation and photoelectron spectroscopy. 

In this connection, a very recent paper by Allinger (8) should be mentioned. A force field has been developed to permit molecular mechanics calculations on various molecular structures of elemental sulfur. The conformational characteristics of sulfur rings containing five to 12, 14, 16, 18, or 20 sulfur atoms have been examined. Comparison with experimental data is made in all cases where such data exist, and predictions are made for other cases. Ab initio molecular orbital calculations using an STO-3G basis set were carried out for cyclohexasulfur and are consistent with the molecular mechanics calculations in indicating that the chair and the twist forms are two stable conformations, with the chair about 15 kcal/mol more stable while the boat (C2t,) is a twist rotational transition state. Calculation of possible conformations of the pro-... 

The molecular structure of 1,3,5-triazine in the gas phase was determined from electron diffraction, infrared and Raman data and 4-21G force field calculations C—N bond length = 1.338 A, C—H = 1.106A, CNC bond angle = 113.9°, NCN= 126.1°, and HCN= 116.9° <86JST(147)321>. The geometries of 1,3,5-triazine and its protonated form, along with other azines, have been fully optimized at the STO-3G, 3-21G and 6-31G levels <87JST(35)135>. 

Steric energy in force fields, 29 STO-nG basis set, 158 Stochastical d)mamics, 389 Stretch energy, in force field energies, 8 Strong Orthogonality (SO), in generalized valence bond metiiods, 202 Sum Over States (SOS) methods, 240 Superoperators, 259... 

The (5s4p2d/3slp) Slater orbital (STO) basis has been used in a study of the quartic force field of H20. These calculations are done using SCF, SD-CI, and with various many-body models. The theoretical results agree well with the experimental force constants, with the many-body values showing better agreement than SD-CI. In fact, the most recent experimental and normal coordinate study revises several of the previously accepted force constants to be more consistent with these theoretical calculations. All of the cubic and quartic constants are determined from the calculations, while the experimental studies typically set many of these constants to zero to facilitate obtaining the force field from the normal coordinate analysis. Hence, the computed SDQ-MBPT(4) quartic force field for H2O is used as input to the local description of H2O in the 0 + H2O surface fit. This is described in detail in section IV. 

The above analyses is based on the thermodynamical theory, while G. Rupprecht et al. and Johnson also diseussed the origin of such field-dependent behavior according to the ion oscillating in a lattice anharmonic potential in perovskites [3,42]. It has been concluded that the anharmonic restoring forces on the Ti ion when it is displaced from its equilibrium position, is responsible for the dielectrie tuning in BST and STO. G. Rupprecht et al. also evaluated the nonlinear constant of A(= in Eq. 6. Their theoretical results indicated... 

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