Geometric derivatives of excitation energies using SCF and DFT

There is increasing interest in using the methods of time-dependent density functional theory to calculate electronic excitation energies. We have implemented an analytic gradient method to find the geometric derivatives of the excitation energies. When added to the gradient for the ground state, this yields the excited-state energy derivatives. This enables the efficient generation and searching of excited-state potential energy surfaces to obtain excited-state geometries and other properties. The initial implementation is for SCF methods and for the local density approximation. Some examples of excited-state geometry optimizations are given.