Electron donor‐acceptor complexes: Evaluation of MNDO as a computational tool to probe intermolecular interactions

Abstract

Donor-acceptor pairs form EDA complexes that exist as conformational isomers exhibiting different ground-state and photochemical properties. We have sought a rapid, general, and accurate quantum mechanical computational method to generate potential energy surfaces that are representative of the donor-acceptor intermolecular interactions at the self-consistent field (SCF) level. The semiempirical molecular orbital (MO) method MNDO has been compared to ab initio methods to assess its behavior with respect to energy, dipole moment and ionization potential shifts. MNDO correctly distinguishes between repulsive and bound EDA complex states at the SCF level and produces potential curves that are smooth and free of spurious minima or cusps. MNDO curves are systematically more repulsive than those for ab initio sm-3G calculations; calculated interaction energies exhibit a mean absolute deviation of 2.90 kcal/mol. MNDO appears to provide a reliable qualitative estimate of the nondispersion portion of the interaction energy. Limitations and errors arising from minimal basis sets, single determinants, and neglect of dispersion are discussed.

Molecular Clusters of π-Systems: Theoretical Studies of Structures, Spectra, and Origin of Interaction Energies

“…Much attention has recently been focused on the interactions between π-systems, especially the aromatic π-systems, ,,,− because of their relevance in the stacking of base pairs in DNA, , protein structure, − molecular recognition, , and properties in condensed phases. , An equal amount of literature is also available on the interactions prevailing between the olefinic π-systems. − In this brief account on π−π interactions, apart from highlighting the new theoretical insights, we also compare the olefinic π−π and aromatic π−π interactions.…”

“…235,236 An equal amount of literature is also available on the interactions prevailing between the olefinic π-systems. [237][238][239][240][241][242][243][244][245][246][247][248][249][250][251][252] In this brief account on π-π interactions, apart from highlighting the new theoretical insights, we also compare the olefinic π-π and aromatic π-π interactions.…”

Charge-Transfer Complexes: Stringent Tests for Widely Used Density Functionals

“…An important number of quantum mechanical studies − have been made in order to understand the nature of the charge-transfer interactions. These studies used semiempirical or Hartree−Fock (HF) methods.…”