title: An efficient algorithm for energy gradients and orbital optimization in valence bond theory.
abstract: An efficient algorithm for energy gradients in valence bond theory with nonorthogonal orbitals is presented. A general Hartree-Fock-like expression for the Hamiltonian matrix element between valence bond (VB) determinants is derived by introducing a transition density matrix. Analytical expressions for the energy gradients with respect to the orbital coefficients are obtained explicitly, whose scaling for computational cost is m(4), where m is the number of basis functions, and is thus approximately the same as in HF method. Compared with other existing approaches, the present algorithm has lower scaling, and thus is much more efficient. Furthermore, the expression for the energy gradient with respect to the nuclear coordinates is also presented, and it provides an effective algorithm for the geometry optimization and the evaluation of various molecular properties in VB theory. Test applications show that our new algorithm runs faster than other methods.
authors.affiliation: The State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, China.
authors.forename: Lingchun
authors.initials: L
authors.lastname: Song
authors.forename: Jinshuai
authors.initials: J
authors.lastname: Song
authors.forename: Yirong
authors.initials: Y
authors.lastname: Mo
authors.forename: Wei
authors.initials: W
authors.lastname: Wu
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D008956:Models, Chemical; D011789:Quantum Theory