Accurate ab initio determination of the adiabatic potential energy function and the Born–Oppenheimer breakdown corrections for the electronic ground state of LiH isotopologues

Abstract

High level ab initio potential energy functions have been constructed for LiH in order to predict vibrational levels up to dissociation. After careful tests of the parameters of the calculation, the final adiabatic potential energy function has been composed from: (a) an ab initio nonrelativistic potential obtained at the multireference configuration interaction with singles and doubles level including a size-extensivity correction and quintuple-sextuple ζ extrapolations of the basis, (b) a mass-velocity-Darwin relativistic correction, and (c) a diagonal Born-Oppenheimer (BO) correction. Finally, nonadiabatic effects have also been considered by including a nonadiabatic correction to the kinetic energy operator of the nuclei. This correction is calculated from nonadiabatic matrix elements between the ground and excited electronic states. The calculated vibrational levels have been compared with those obtained from the experimental data [J. A. Coxon and C. S. Dickinson, J. Chem. Phys. 134, 9378 (2004)]. It was found that the calculated BO potential results in vibrational levels which have root mean square (rms) deviations of about 6-7 cm(-1) for LiH and ∼3 cm(-1) for LiD. With all the above mentioned corrections accounted for, the rms deviation falls down to ∼1 cm(-1). These results represent a drastic improvement over previous theoretical predictions of vibrational levels for all isotopologues of LiH.

Theory and application of explicitly correlated Gaussians

“…This table shows that only ECG-based approaches have achieved hartree-level accuracy for this system. However, the multireference (MR)-CISD result of À8:070 792 hartree at R ¼ 3:000 bohr reported by Holka et al (2011) is 239 hartree below the best ECG value and about 50 times outside its estimated uncertainty. The reasons for this discrepancy are unclear at the moment.…”

“…However, the most TABLE IX. The total electronic energy (in hartree) of the LiH molecule at R ¼ 3:015 a 0 , except the last entry, (Holka et al, 2011), which used R ¼ 3:000 a 0 . accurate value of the interaction energy at the potential minimum (R ¼ 5:6 a 0 ) was obtained using the direct variational optimization of the full four-electron ECG function .…”

Algorithms for calculating mass-velocity and Darwin relativistic corrections with n-electron explicitly correlated Gaussians with shifted centers

“…The code has been tested in the calculations involving the H 2 and LiH molecules. For the former system, the results are compared with the calculations of Wolniewicz 18 and for the latter system with the calculations performed by Holka et al 19 The present calculations of the MV and D corrections of the two systems have been performed for same selected internuclear distances sampling the full range of the corresponding potential energy curves.…”

“…The literature data which can be used for comparison are much more limited than in the case of the H 2 molecule. The most recent calculations of the relativistic corrections for the LiH molecule are those of Holka et al 19 However, their calculations were performed using …”

Electronic structure and time-dependent description of rotational predissociation of LiH

“…Special investigations were devoted to dipole moments 24,25 and ionic states of LiH 26,27,28 . Recently, Tung et al 29 and Holka et al 30 performed very accurate calculations of the ground and some excited state potential curves.…”