A quantum Monte Carlo study of thorium halide molecules

We present electronic structure calculations of thorium halide molecules, namely, a series of $ ThCl_n $ and $ ThBr_n $ (n=1,2,3,4) systems. We calculate the bond dissociation energies for the sequence of the following dissociation reactions: $ ThCl_n -> ThCl_{n-1} + Cl $ and $ ThBr_n -> ThBr_{n-1}+Br $. We apply both large core and small core energy-consistent pseudopotentials for thorium atom and we employ DFT GGA and hybrid functionals for energies and geometry calculations. For high accuracy energies we use the fixed-node diffusion Monte Carlo (DMC) method. In DMC calculations we employ both single- and multi-reference trial wave functions in order to test the quality of the nodal surfaces. We study the dissociation energies with regard to different multiplicities of the $ ThX_{n} $ molecules and the different behavior of the bromides with respect to chlorides. We compare our results with hybrid DFT methods and experimental values. Supported by DOE and NSF.