Wavefunction theory and density functional theory analysis of ground and excited electronic states of TaB and WB

Several low-lying electronic states of TaB and WB molecules were studied using ab initio multireference configuration interaction (MRCI), Davidson corrected MRCI (MRCI+Q), and coupled cluster singles doubles and perturbative triples [CCSD(T)] methods. Their full potential energy curves (PECs), equilibrium electron configurations, equilibrium bond distances (res), dissociation energies (Des), excitation energies (Tes), harmonic vibrational frequencies (omega es), and anharmonicities (omega exes) are reported. The MRCI dipole moment curves (DMCs) of the first 5 electronic states of both TaB and WB are also reported and the equilibrium dipole moment (mu) values are compared with the CCSD(T) mu values. The most stable 13 Pi (1 sigma 22 sigma 23 sigma 11 pi 3) and 15 Delta (1 sigma 22 sigma 23 sigma 11 pi 21 delta 1) electronic states of TaB lie close in energy with similar to 62 kcal mol-1De with respect to the Ta(4F) + B(2P) asymptote. However, spin-orbit coupling effects make the 15 Delta 0+ state the true ground state of TaB. The ground electronic state of WB (16 Pi) has the 1 sigma 22 sigma 13 sigma 11 pi 31 delta 2 electron configuration and is followed by the excited 16 Sigma+ and 14 Delta states. Finally, the MRCI De, re, omega e, and omega exe values of the 13 Pi state of TaB and 16 Pi and 14 Delta states of WB are used to assess the density functional theory (DFT) errors on a series of exchange-correlation functionals that span multiple-rungs of the Jacob's ladder of density functional approximations (DFA). Full potential energy curves, electronic configurations, spectroscopic parameters, dipole moments, and energetics of ground and excited electronic states of TaB and WB were studied using MRCI, MRCI+Q, CCSD(T), and DFT levels of theory.