Paired-Permanent-Determinant Algorithm for Nonorthogonal Valence Bond Method

PAIRED-PERMANENT-DETERMINANT ALGORITHM FOR NONORTHOGONAL VALENCE BOND METHOD 

In this section, a new function, called paired-permanent-determinant (PPD), is introduced, which is an algebrant. An overlap matrix element in the spin-free VB method may be obtained by evaluating a corresponding PPD, while the Hamiltonian matrix element is expressed in terms of the products of electronic integrals and sub-PPDs. 

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