نتایج جستجو برای: روش ab initio
تعداد نتایج: 412285 فیلتر نتایج به سال:
Ž . The MELD program is employed to evaluate the Slater average potential v r felt by an electron at the point r within an atom. The characteristic radius R of the atom is then Ž . defined by the classical turning point equation v R I, where I denotes the first ionization potential of the atom. The atomic radii defined in this way have a close correlation with the van der Waals atomic radii. 19...
An ab initio calculation of a secondary isotope effect on a bond length has been carried out for the first time. Single determinant molecular orbital computations indicate that the mean C-C bond length at O"K is longer in C,H6 than in C,D6 by 0.0015 A. A comparison with model calculations supports a steric interpretation in which H atoms act as if they are bulkier than 0 atoms owing to their la...
Starting from the 1980s and onwards, Valence Bond theory has been enjoying renaissance that is characterized by the development of a growing number of ab initio methods, and by many applications to chemical reactivity and to the central paradigms of chemistry. Owing the increase of computational power of modern computers and to significant advances in the methodology, valence bond theory begins...
An algorithm for calculating the scattering factors of atomic fragments in molecules as defined by the Stockholder recipe is presented. This method allows the calculation, from ab initio molecular wave functions, of structure factors including individual anisotropic atomic temperature factors. These structure factors agree with the model used in most leastsquares multipole-refinement procedures...
The factors that need to be taken into account to achieve spectroscopic accuracy for triatomic molecules are considered focusing on H3 + and water as examples. The magnitude of the adiabatic and non-adiabatic corrections to the Born–Oppenheimer approximation is illustrated for both molecules, and methods of including them ab initio are discussed. Electronic relativistic effects are not importan...
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