The Lennard-Jones lecture: the value of very-high-accuracy calculations in quantum chemistry

Abstract

Five recent topics under research at Cambridge in ab initio quantum chemistry are reported: (a) the latest developments in methods for full CI calculations, (b) the convergence of the Møller–Plesset perturbation-theory series at the RHF and UHF level, using H₂O and NH₂ as examples, with energies up to 24th order, (c) a new way to calculate Møller–Plesset energy gradients and second derivatives, the latter needing only the solution of the first-order CPHF equations, (d) some calculations using the quantum Monte Carlo method compared with standard CI calculations and (e) high-accuracy calculations on Be₂, Be₃ and Be₄ to demonstrate the value of such research.