Taming the First-Row Diatomics: A Full Configuration Interaction Quantum Monte Carlo Study

The initiator full configuration interaction quantum Monte Carlo (i-FCIQMC) method has recently been developed as a highly accurate stochastic electronic structure technique. It has been shown to calculate the exact basis set ground state energy of Small molecules, to within modest stochastic error bars,. using tradable computational cost. Here, we use this technique. to elucidate, an often troublesome series of first row diatomics consisting. of Be-2, C-2, CN, CO, N-2, NO, O-2, and F-2. Using i-FCIQMC, the dissociation energies of these molecules are obtained. almost entirely to within chemical accuracy of. experimental results Furthermore, the i-FCIQMC calculations are performed. in a relatively black box manner, without any a priori knowledge or specification of the Wave function. The Size consistency of i-FCIQMC is also demonstrated with regards to these diatomics at their more multiconfigurational stretched geometries. The cleat and simple i-FCIQMC wave functions obtained for these systems are then compared and investigated to demonstrate the dynamic identification of the dominant determinants contributing to significant static correlation. The appearance and nature of such determinants is shown to provide insight into both the i-FCIQMC algorithm and the diatomics themselves.