# HYDMATEL: a code to calculate matrix elements for hydrogen-like atoms

## Description

Abstract Recursion relations for determining radial matrix elements of r-dependent operators between hydrogenic wavefunctions are derived using a technique based on the hypervirial theorem along with a second quantization formalism. These expressions have been included in the program HYDMATEL, and this code is valid for both diagonal and off-diagonal matrix element calculations with no limitation on the values of the n and l quantum numbers or on the power of the operator. Title of program: HYDMATEL Catalogue Id: ACLO_v1_0 Nature of problem Many problems in atomic physics need the calculation of matrix elements for r-dependent operators. The calculation of these elements could be carried out by resolving the integral analytically, but when n is much greater than l, Gordon's formula or other analytically expanded formulae are not only hard to use, but have no numerical validity for large n due to successive cancellations between positive and negative terms. Several alternative methods have therefore been developed: asymptotic expans ... Versions of this program held in the CPC repository in Mendeley Data ACLO_v1_0; HYDMATEL; 10.1016/0010-4655(93)90174-B This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2019)