Abstract:
Although ab initio many-body methods can provide accurate predictions for most small systems, substantial effort is devoted to design and develop fairly accurate and computationally efficient ‘packageable’ methods for treating large molecular systems, where packageable implies a method that can be incorporated into widely distributed suites of electronic structure programs. Here, we provide further tests and illustrations of our recently developed improved virtual orbital-complete active space configuration interaction (IVO-CASCI) method, which is designed to supplant CIS and CASSCF approaches in electronic structure ‘packages’ because of greater computational efficiency without sacrificing accuracy. The IVO-CASCI method is used here to compute the ground, excited, positive, and negative ion potential energy curve of hydrogen fluoride. Additional dynamical correlation is incorporated by using IVO-CASCI wavefunctions as the initial approximation in selected further effective valence shell Hamiltonian computations for HF and its ions. The excellent agreement between the theory, experiment, and some benchmark calculations for several ground, excited, and ion states of HF reinforces the claim that the IVO-CASCI method is a viable alternate packageable many-body method for ground, excited, and other open-shell states of small to large molecular systems.
