Analytical gradient for geometry optimizations of (H2 O)n- clusters as described by the PM1 polarizable model

Expressions for the analytical gradients of the PM1 polarization model for describing the interaction of excess electrons with water clusters are reported. For the (H2 O)45- cluster, evaluation of the gradient by use of the analytical expressions lead to a factor of five speedup over numerical evaluation of the gradient. © 2008 Elsevier B.V. All rights reserved.