Role of charge transfer configurations in LaMnO3, CaMnO3, and CaFeO3

Abstract

A simple scheme is proposed to analyze the N-electron wave function obtained in embedded cluster calculations in valence bond terms such as ligand-to-metal charge transfer and non-charge-transfer determinants. The analysis is based on a unitary transformation of pairs of natural orbitals to optimal atomiclike orbitals. The procedure is applied to compare the degree of ionicity in NiO and MnO and to explain the existence or absence of Jahn-Teller distortions in LaMnO3, CaMnO3, and CaFeO3. The authors find that the ground state of LaMnO3 is dominated by non-charge-transfer configurations, whereas the charge transfer configurations dominate the ground state wave function in the other two perovskites.

Why sp2‐like nanosilicons should not form: Insight from quantum chemistry

“…Thus, the most popular complete‐active‐space‐self‐consistent‐field (CASSCF) methods,6 which deal correctly with diradicals and some dinuclear magnetic complexes (see comprehensive review7), cannot handle systems with larger number of odd electrons due to a huge number of configurations generated in the active space of the system. To imagine arising technical difficulties, it is worthwhile to cite,7 “If there are “ m ” singly occupied orbitals on each of “ n ” identical centers, then 2 mn Slater determinants can be formed by assigning spins up or down each of the “ nm ” orbitals.” So that no CASSCF type approach, including a simplified embedded‐cluster CASSCF supplemented by the complete active space second‐order perturbation theory (CASPT2),8 seems feasible for many‐odd electron systems such as, say, fullerenes. That is why addressing single‐determinant approaches turns out to be the only practically meaningful alternate.…”

Magnetic bistability: From microscopic to macroscopic understandings of hysteretic behavior usingab initiocalculations

“…2͒. 25 This transformation leaves any observable expectation value unchanged and affords a valence-bond ͑VB͒type analysis.…”

Ab initioabsorption spectrum of NiO combining molecular dynamics with the embedded cluster approach in a discrete reaction field

“…This active space offers a solid footing to describe the electronic ground state of NiO (Ref. 100) and the excited states arising from internal Ni d-d excitations and from the lowest LMCT excitations. The so-obtained zero-order wave function is further improved by the aforementioned CASPT2 approach, a second-order perturbation treatment of the remaining dynamic electron correlation.…”