An optimized procedure for reducing the size of available multipole pseudospectra

A simple technique is suggested for representing frequency-dependent atomic and molecular multipole polarizabilities through contracted expansions obtained by reducing the size of available pseudospectra, collecting contributions coming from excited pseudostates. Each optimized contraction is accomplished by minimizing the square difference, suitably integrated over frequency, between the corresponding extended and reduced expansions. Reported numerical results, from calculations performed on a ground-state hydrogen atom, confirm the reliability of reduced pseudospectra in faithfully representing polarizabilities over the entire range covered by the frequency and for accurately evaluating related interactive dispersion constants.