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The electronic spectrum of AgBr 2 : Ab initio benchmark calculations on the 2 Π u and 2 Σ u + charge transfer states including spin‐orbit effects
Author(s) -
RamírezSolís A.
Publication year - 2012
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.24183
Subject(s) - ab initio , atomic physics , ground state , chemistry , valence (chemistry) , complete active space , ab initio quantum chemistry methods , mulliken population analysis , hamiltonian (control theory) , physics , basis set , density functional theory , computational chemistry , molecule , mathematical optimization , mathematics , organic chemistry
The 2 Π u and 2 Σ u + charge transfer (CT) states of AgBr 2 have been studied through benchmark ab initio HF, complete active space SCF, CASPT2, NEVPT2, and averaged coupled pair functional (ACPF) multireference calculations using especially developed valence basis sets to study the transition energies, geometries, vibrational frequencies, and Mulliken charges. The spin‐orbit (SO) effects have been included through the effective Hamiltonian formalism using the ACPF energies as |ΛSΣ> diagonal elements. The equilibrium Ag–Br distance for both CT states is larger than that of the X 2 Π g ground state. The ACPF adiabatic excitation energies of the 2 Π u and 2 Σ u + states are 4620 and 7006 cm ‐1 , respectively. Using previous ACPF benchmark studies showing that the 2 Δ g ligand field (LF) state lies more than 20,000 cm ‐1 above the ground state, these new results lead to the following energetic ordering for the five lowest electronic states of AgBr 2 : X 2 Π g , 2 Σ g + , 2 Π u , 2 Σ u + , and 2 Δ g , in sharp contradiction with Hartree–Fock theory. When considering the coupling of the LF and CT states, the inclusion of the SO effects leads to a pure Ω = 3/2 (X 2 Π g ) ground state, Ω = 1/2 (92% 2 Π g + 8% 2 Σ g + ) A state, Ω = 3/2 (pure 2 Π u ) B state, Ω = 1/2 (68% 2 Π u +32% 2 Σ u + ) C state, Ω = 1/2 (8% 2 Π g + 92% 2 Σ g + ) D state, and an Ω = 1/2 (32% 2 Π u + 68% 2 Σ u + ) E state. We present here what we consider the most complete and accurate account of the electronic spectrum of AgBr 2 . © 2012 Wiley Periodicals, Inc.