Ab Initio Ground‐State Potential Energy Function and Vibration‐Rotation Energy Levels of Aluminum Monohydride

Abstract

The accurate ground‐state potential energy function of aluminum monohydride (AlH) has been determined from ab initio calculations using the multireference averaged coupled‐pair functional (MR‐ACPF) method in conjunction with the correlation‐consistent core‐valence basis sets up to septuple‐zeta quality. The vibration‐rotation energy levels of the two isotopologues, AlH and AlD, were predicted to near the “spectroscopic” accuracy. The importance of electron correlation beyond the MR‐ACPF level of approximation, the scalar relativistic, spin‐orbit, adiabatic, and nonadiabatic effects was discussed. © 2019 Wiley Periodicals, Inc.

Ab initio characterization of the aluminum dimer in its X3Πu and A3∑g− electronic states

“…The CASSCF wave function of Al 2 included thus all excitations of 6 valence electrons in 26 molecular orbitals. As shown in the previous theoretical studies on aluminum monohydride, AlH, [25,26] the configuration interaction treatment based on such a large active space gave the predictions of molecular properties of AlH in near perfect agreement with the full configuration interaction (FCI) treatment. In the generation of the CASSCF wave functions, the 1s-, 2s-, and 2p -like core orbitals of the aluminum atoms were optimized, but they were kept doubly occupied.…”

“…The spin‐orbit splitting is predicted at the dissociation limit to be 115 cm −1 , compared with the corresponding experimental value [ 32 ] of 112.061 cm −1 for the aluminum atom in its ground state. In the previous study on AlH, [ 26 ] the spin‐orbit effects were investigated at the corresponding level of theory, MRCI+Q/aug‐cc‐pCVQZ(uncontracted), albeit using the extended active space instead of the full‐valence one. At the dissociation limit, the spin‐orbit splitting was predicted there to be 108 cm −1 .…”

“…The valence cc‐pV( n + d)Z basis sets up to sextuple‐zeta quality were developed by Dunning et al [ 27 ] The largest basis set for aluminum available in the literature, cc‐pV(6 + d )Z, contains the primitive functions contracted to The cc‐pV(7+ d )Z basis set was developed for the study on AlH. [ 26 ] This basis set contains the primitive functions contracted to Because the MOLPRO package cannot handle functions higher than i , the polarization function was omitted in all subsequent calculations. The diffuse functions, up to the basis set of sextuple‐zeta quality aug‐cc‐pV(6 + d )Z, were taken from the literature.…”

Ab Initio Potential Energy Surface and Vibration–Rotation Energy Levels of Aluminum Monohydroxide

“…Calculations of the molecular parameters of AlOH closely follow those reported recently for magnesium monohydroxide . The electronic energy of AlOH was determined using the conventional coupled-cluster method including single and double excitations and a perturbational correction due to connected triple excitations, CCSD­(T). − The one-particle basis sets employed were the correlation-consistent valence basis sets up to septuple-zeta quality, cc-pV n Z ( n = D–7). − The outer-core 2s- and 2p-like orbitals of aluminum were treated as valence, and therefore, the basis sets for aluminum were augmented with tight functions (C). Because the natural charge at the oxygen atom of AlOH was estimated to be – 1.3 e , the basis sets for oxygen were augmented with diffuse functions (aug).…”

“… 15 − 18 The one-particle basis sets employed were the correlation-consistent valence basis sets up to septuple-zeta quality, cc-pV n Z ( n = D–7). 19 − 24 The outer-core 2s- and 2p-like orbitals of aluminum were treated as valence, and therefore, the basis sets for aluminum were augmented with tight functions (C). Because the natural charge at the oxygen atom of AlOH was estimated to be – 1.3 e , the basis sets for oxygen were augmented with diffuse functions (aug).…”