Relativistic and electron correlation effects for molecules of heavy elements: Ab initio fully relativistic coupled-cluster calculations for PbH4

Ab initio fully relativistic all-electron Dirac–Fock (DF) and nonrelativistic (NR) Hartree–Fock (HF) limit self-consistent field (SCF) benchmark molecular calculations are reported for the tetrahedral (Td) PbH4 at various Pb–H bond distances. Our fully relativistic Dirac–Fock and nonrelativistic HF calculations predict for a PbH4 bond distance of 1.75 and 1.82 A, respectively. Both our DF and NR HF limit SCF calculations predict the ground state of PbH4 (Td) to be bound, with the predicted atomization energy (Ae) of 7.20 and 8.63 eV, respectively. There are antibinding effects due to relativity of ∼1.4 eV to the predicted atomization energy (Ae) of PbH4. Our relativistic four-component coupled-cluster singles and doubles (RCCSD) calculations, which correlate 50 electrons and include 302 active molecular spinors with energies up to ∼46 a.u. in the active space predict the relativistic second-order Moller-Plesset (RMP2), RCCSD and RCCSD (T) (RCCSD plus the triple excitation correction included perturbationally) correlation energies as −1.271, −1.161, and −1.186 hartree, respectively. The contribution of the RMP2, RCCSD, and RCCSD (T) electron correlation energies toward the atomization energy of PbH4 as predicted by our above-mentioned CC calculation is 3.78, 4.22, and 4.30 eV, respectively. We predict the NR and relativistic MP2, CCSD, and CCSD (T) atomization energies (Ae) for PbH4 at the optimized PbH bond distances as 12.72, 12.90, 1.77 and 10.98, 11.42, and 11.50 eV, respectively. With the inclusion of both the electron correlation and effects of relativity, we predict the atomization energy for PbH4 to be ∼10–11 eV. This should encourage experimentalists to devise new synthetic methods to prepare plumbane, so that its chemical and physical properties can be investigated as in the case of its lighter congeners. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004