Off-diagonal elastic constants

Off-diagonal elastic constants for stretching of bonds incident to the central... 

By contrast, for the 14-electron complexes (nontransition nonmetals) the symmetries of the frontier orbitals are I n = aig and rL = l u and the tensor product Th rL = a g 11 = 11 so that only the transition density corresponding to the representation t survive. Analogous moves allow us to conclude that the off-diagonal elastic constant for stretching the /.ran.s-bonds has the form ... 

The models thus built remain mechanistic ones, but they naturally take into account those important features of the electronic structure, which in a standard formulation, would require innumerable parameterizations for more and more tricky force fields, whose form remains without any fundamental basis. For example, off-diagonal elastic constants obtained thus do not assume the angular dependent form like... 

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