نتایج جستجو برای: محاسبات ab initio
تعداد نتایج: 54800 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...
[1] The elastic constants of post-perovskite of chemical composition Mg0.9375Fe0.0625SiO3 and Mg0.8750Fe0.1250SiO3 have been calculated at 0 K and 136 GPa using ab initio methods. For both compositions studied, iron remains in a high-spin state below 180 GPa at 0 K. The effect of spin state on elastic properties is small. Logarithmic derivations of isotropic wave velocities and density with res...
The enormous developments of computer technologies allow the broad employment of ab initioMO theory in foldamer research. In this review, we demonstrate the efficiency and reliability of ab initioMO methods for the description of the helix formation in oligomers of w-amino acids on the basis of representative examples. Thus, ab initio MO theory successfully accompanies foldamer research by conf...
In this paper size effects, growth orientation and also doping by Ammonia molecule (NH3) on the carbon nanowire properties with saturated diamond structure by (DNw:H) have been investigated. This study was carried out using DFT theory and Kohn-Sham equation by self-consistent field (SCF) that performed by local density approximation (LDA). The nanowires morphology is cylindrical with [111] grow...
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