Theoretical investigation of the lithium2p←2sphotoabsorption spectra perturbed by atomic hydrogen

Abstract

This work proposes a theoretical study of the Li(2p ← 2s) photoabsorption spectra perturbed by ground hydrogen atoms. The temperature effect on the far-wing spectra is examined in the temperature range 4000-20 000 K. For this purpose, the ground and excited LiH potential curves and the transition dipole moments that connect them are constructed from ab initio data. The investigation shows that the profile spectra are dominated at all temperatures by the singlet A ← X transitions and exhibit in the red wing a satellite structure near the wavelength 1000 nm. The spectra revealed also the appearance beyond 14 000 K of a second satellite structure in the blue wing close to the wavelength 510 nm originating from the triplet c ← a transitions.

Diabatic-At-Construction Method for Diabatic and Adiabatic Ground and Excited States Based on Multistate Density Functional Theory

“…We compare the MSDFT potential energy curves to MS-CASPT2 results; both the qualitative trends and quantitative results from MS-CASPT2 calculations agree well with more complete or more accurate studies. − ,− The present MSDFT method does not involve the high cost of a SA-CASSCF computation, but it includes all dynamic correlation at the stage of diabatic (basis) state construction, yielding results comparable or better than the more expensive MS-CASPT2 calculation. Furthermore, the number of configurations in the active space is smaller in the present method (12 determinants vs 45 in the (2,9)-CAS) – an advantage of the DTS scenario).…”

“…69–71,73–75 The present MSDFT method does not involve the high cost of a SA-CASSCF computation, but it includes all dynamic correlation at the stage of diabatic (basis) state construction, yielding results comparable or better than the more expensive MS-CASPT2 calculation. Furthermore, the number of configurations in the active space is smaller in the present method (12 determinants vs 45 in the (2,9)-CAS) – an advantage of the DTS scenario).…”

“…LiH is chosen because this simple system provides a challenging case for treating avoided state crossings, spanning a coordinate range from the bonding region to more than 10 Å in interatomic separation, and the states of LiH have been extensively studied both experimentally 71,75 and theoretically so they provide a good case for validation of the present method. 69–71,73,74 …”

“…The LiH molecule, being the second simplest two-electron chemical bond (after the hydrogen molecule), has been intensively investigated; it has a strong ionic–covalent mixing and a prominent ionic–covalent curve crossing. − In the following, we illustrate the block-localization procedure to form the DAC states by considering the four lowest 1 ∑ + states of LiH, which we describe by MSDFT. LiH is chosen because this simple system provides a challenging case for treating avoided state crossings, spanning a coordinate range from the bonding region to more than 10 Å in interatomic separation, and the states of LiH have been extensively studied both experimentally , and theoretically so they provide a good case for validation of the present method. − ,, …”

Diabatic States at Construction (DAC) through Generalized Singular Value Decomposition

“…In the present discussion, it provides an interesting example to model multiple adiabatic states by a diabatic representation. The dissociation curves of LiH have been intensively investigated, − and we have shown that it is sufficient to use seven VB basis states in MSDFT to describe quantitatively the energies of the four lowest singlet states in comparison with experiments and MS-CASPT2 calculations . The seven VB configurations, in order of increasing energy (Supporting Information), except the first, include the |Ψ ion [(Li + )­(H – )]⟩ ionic structure, the dissociation limits of the Li atom in the 2s, 2p, 3s, and 3p states, along with an excited configuration for the H­(2s) atom and the reverse ionic configuration |Ψ – [(Li – )­(H + )]⟩.…”