Calculation of molecular structures

Intensive use of cross-terms is important in force fields designed to predict vibrational spectra, whereas for the calculation of molecular structure only a limited set of cross-terms was found to be necessary. For the above-mentioned example, the coupling of bond-stretching (f and / and angle-bending (B) within a water molecule (see Figure 7-1.3, top left) can be calculated according to Eq. (30). 

Finley, J. W., Stephens, P. J., 1995, Density Functional Theory Calculations of Molecular Structures and Harmonic Vibrational Frequencies Using Hybrid Density Functionals , J. Mol. Struct. (Theochem), 357, 225. 

Force-field methods, calculation of molecular structure and energy by, 13,1 Free radical chain processes in aliphatic systems involving an electron-transfer reaction, 23, 271 Free radicals, and their reactions at low temperature using a rotating cryostat, study of, 8. I Free radicals, identification by electron spin resonance, 1, 284... 

Force-field methods, calculation of molecular structure and energy by, 13, 1... 

Force-field methods, calculation of molecular structure and energy by, 13, 1 Free radical chain processes in aliphatic systems involving an electron-transfer reaction, 23, 271... 

Calculation of molecular structure at successive small time intervals using a molecular mechanics force field with the shifts determined using Newton s laws of motion. 

J. W. Finley and P. J. Stephens, Density functional theory calculations of molecular structures and harmonic vibrational frequencies using hybrid density functionals, J. Mol. Struc. (Theochem.), 357 (1995) 225-235. 

The period during and about ten years after WWII saw the beginnings of the development of automatic computing machinery. Although early workers made heroic efforts in many calculations, computers allowed calculations of molecular structure that were far too tedious to undertake by hand or to expect reliable results. The new computers thus allowed many of the quantitative procedures worked out earlier to be checked and accepted... 

Vinylamine (R1 = R2 = R3 = H) is the simplest primary enamine. It was prepared by gas-phase pyrolysis of ethylamine and characterized by its microwave spectrum which led to a crude determination of its molecular geometry56. The interesting question refers to the extent of planarity or tetrahedral geometry of the amino group and this is discussed in the section on calculations of molecular structures. 

Allinger NL (1976) Calculation of molecular structure and energy for force-field methods. Adv Phys Org Chem 13 2-75... 

In this enterprise, it rapidly becomes apparent that the sort of approach that has been so fruitful for quantum theory calculations of molecular structures cannot succeed with reactions. For a molecular structure calculation, all that is really required is to determine the arrangement of electrons that corresponds to the particular fixed geometric arrangement of nuclei that represents the stable geometry of the molecule. 

We do not review the calculation of molecular structure factors as this has been described in text books [48]. However, we note that for the calculation of molecular structure factors, knowledge of atomic scattering factors is fundamental. The atomic scattering factors /atomic used in most modern X-ray refinement packages were fitted by Cromer and Mann [49] to the functional form... 

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