L2 golden rule-RRG combined method for resonance energies and widths

A new golden rule-recursive residue generation (RRG) combined method for calculating the positions and widths of predissociation resonances is formulated. The method uses a golden-rule-like formula but avoids explicit computation of full Hamiltonian eigenvectors and is based upon the recursive generation of residues of the Greenʹs function. The eigenvectors of the reduced Hamiltonian matrix are used to prepare the initial starting vector of the recursion procedure. Combination of the golden rule and RRG methods is well suited for large Hamiltonian matrices, providing faster execution and requiring less memory than standard methods. A numerical example is presented.