نتایج جستجو برای: valence bond theory
تعداد نتایج: 859522 فیلتر نتایج به سال:
A scheme is presented for calculating the heats of formation of adsorbed species on metal surfaces using only two pieces of gas phase data, both of which are available from either theory or experiment. Using this quasiempirical valence bond (QVB) approach, heats of adsorption and adsorbate-surface bond strengths can be estimated, yielding predictions of surface thermochemistry and reaction mech...
Ž . Ž . A semi-empirical valence bond VB method, called VBDFT s , is described and applied to C H conjugated n nq2 hydrocarbons. The method is a Huckel-type VB scheme with energies scaled to density functional theory energies based on a ̈ single parameter; the matrix element l due to spin transposition between bonded atoms. Total energies, excitation energies, resonance and p-bond energies are p...
Quaternary chalcopyrites have shown to exhibit tunable band gaps with changing anion composition. Inspired by these observations, the underlying structural and electronic considerations are investigated using a combination of experimentally obtained structural data, molecular orbital considerations, and density functional theory. Within the solid solution Cu2ZnGeS4-x Se x , the anion bond alter...
Ab initio calculations (Hartree-Fock, generalized valence bond, and configuration interaction), utilizing relativistic core potentials, have been used to follow the oxidative addition of Hz to Pt(PH,),. We find an activation barrier of 2.3 kcal/mol and an exothermicity of 15.9 kcal/mol. From examination of the geometries and wave functions, we find that up to the transition state the H-H bond i...
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An effective Hamiltonian mixed molecular orbital and valence bond (EH-MOVB) method is described to obtain an accurate potential energy surface for chemical reactions. Building upon previous results on the construction of diabatic and adiabatic potential surfaces using ab initio MOVB theory, we introduce a diabatic-coupling scaling factor to uniformly scale the ab initio off-diagonal matrix elem...
Utilization of binary information encoded in the charge configuration of quantum-dot cells (the quantum-dot cellular automata, QCA, paradigm) requires molecule-sized dots for room temperature operation. Molecular QCA cells are mixed-valence complexes, and the evaluation and functionalization of an unsymmetrical heterobinuclear, two-dot, Fe-Ru molecular QCA cell is described. The solid state str...
We report the displacive and order–disorder characters of PbTiO3 analyzed using a classical atomic model which was developed under the inverse relation between the bond length and the bond valence. The ferroelectric phase changes to the paraelectric phase around 700 K, and the histograms of Ti–O and Pb–O bond lengths have three peaks which become a single peak above the phase transition tempera...
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