Comprehensive ab initio calculation and simulation on the low‐lying electronic states of TlX (X = F, Cl, Br, I, and At)

Abstract

The low-lying electronic states of TlX (X=F, Cl, Br, I, and At) are investigated using the configuration interaction based complete active space third-order perturbation theory [CASPT3(CI)] with spin-orbit coupling accounted for. The potential energy curves and the corresponding spectroscopic constants are reported. The results are grossly in good agreement with the available experimental data. The absorption spectra are simulated as well to reassign the experimental bands. The present results are also useful for guiding future experimental measurements.

Padé extrapolated effective Hamiltonians in the Fock space relativistic coupled cluster method

“…It might be worth underlining that the extrapolation had not lead to any irregularities. The corresponding estimates of the equilibrium distances and adiabatic term energies for excited states (Table ) are in a reasonable agreement with the experimental values and seem at least not inferior in accuracy to those from extensive multireference configuration interaction based complete active space third‐order perturbation theory [CASPT3(CI)] calculations of Zou and Liu …”

“…The corresponding estimates of the equilibrium distances and adiabatic term energies for excited states (Table 2) are in a reasonable agreement with the experimental values and seem at least not inferior in accuracy to those from extensive multireference configuration interaction based complete active space third-order perturbation theory [CASPT3(CI)] calculations of Zou and Liu. [74] A separate set of excitation energy calculations taking into account the correlations involving 5s5p subshell was performed with Tl basis set appropriately extended by compact Gaussians [66] to [9s 10p 8d 6f 4g 1h]. The corresponding results marked by the symbols +CV in Table 2 Calculated potential energy functions for the X0 + , A0 + , and B1 states of TlF…”

Λ doubling in the B3Π1 state of TlF

“…The rigorous approach to incorporate the Λ-doubling and higher-order hyperfine structure terms in the Hamiltonian, in a combined fit of the eand f -levels, is seen to describe the energy level structure in the B-state of TlF very well, unambiguously demonstrating that this is an Ω = 1 state. It is remarkable that this state can be so well described by the Hamiltonian of an isolated 3 Π 1 state, even up to rotational energies of 0.25 eV above the lowest level, given the high density of electronically excited states nearby [17,18]. The large value for h 1 would be extraordinary for light diatomics, but might be common for molecules with heavy nuclei.…”

Development and application of the analytical energy gradient for the normalized elimination of the small component method

“…In Table III, exact quasirelativistic 1c-NESC geometries obtained at the NESC/CCSD and bond dissociation energies (D e and D 0 ) calculated at the NESC/CCSD(T) level of theory are listed and compared with results of other calculations as well as the experimental data. [68][69][70] Also summarized in Table III are some NESC/DFT results calculated for the two organic mercury compounds 14 and 15 shown in Fig. 1.…”