An improvement of Davidson's iteration method: Applications to MRCI and MRCEPA calculations

Davidsons method is widely used for finding the lowest eigenvalues of large matrices. Recently, mathematicians have shown that Davidsons derivation could be improved. They have corrected the derivation yielding a new iteration method. In this article this new method is adapted for realistic MRCI and MRCEPA calculations. Results show that the new method converges significantly faster in H2O and O2 with moderately elongated bonds than Davidsons original method. The new method offers new insights into the rate of convergence of Davidsons original method.