Alternative CNDOL Fockians for fast and accurate description of molecular exciton properties.

CNDOL is an a priori, approximate Fockian for molecular wave functions. In this study, we employ several modes of singly excited configuration interaction (CIS) to model molecular excitation properties by using four combinations of the one electron operator terms. Those options are compared to the experimental and theoretical data for a carefully selected set of molecules. The resulting excitons are represented by CIS wave functions that encompass all valence electrons in the system for each excited state energy. The Coulomb-exchange term associated to the calculated excitation energies is rationalized to evaluate theoretical exciton binding energies. This property is shown to be useful for discriminating the charge donation ability of molecular and supermolecular systems. Multielectronic 3D maps of exciton formal charges are showcased, demonstrating the applicability of these approximate wave functions for modeling properties of large molecules and clusters at nanoscales. This modeling proves useful in designing molecular photovoltaic devices. Our methodology holds potential applications in systematic evaluations of such systems and the development of fundamental artificial intelligence databases for predicting related properties.

Molecular orbital model of the influence of interaction between O2 and aluminosilicate sites on the triplet-singlet energy gap and reactivity.

The behavior of O(2) molecule in models of acid aluminosilicate sites on any kind of material was investigated using reliable QM ab initio calculations. The triplet-singlet energy gap of isolated O(2) was calculated at confident levels of theory with different basis sets as a reference. Models of aluminosilicate active sites interacting with oxygen in their singlet and triplet electronic states were considered for two kinds of O(2) arrangements. Geometry optimizations were performed on both non-corrected and corrected BSSE potential energy surfaces, realizing that good modeling of heavy atom-hydrogen interactions is sensitive to BSSE corrections during these processes. Energies were further evaluated at higher level of theory to test tendencies. Singlet oxygen appears more attractive to active aluminosilicate sites than those calculated with triplet oxygen, indicating a source of oxidative efficiency for designed nanostructures containing such molecular residues. It was clearly seen that aluminosilicate groups, appearing ubiquitously in several materials, could reduce the O(2) triplet-singlets energy gap by at least 10 kJ/mol. Some elegant features of oxygen interactions with such sites were further analyzed by means of the atoms in molecules (AIM) theory.

A DFT periodic study on the interaction between O2 and cation exchanged chabazite MCHA (M = H+, Na+ or Cu+): effects in the triplet-singlet energy gap.

O(2) adsorption in proton, sodium and copper exchanged chabazite has been studied using periodic and cluster approaches by means of density functional theory. The Grimme's correction has been used to include the dispersion contribution to B3LYP. Two cation locations have been considered: one with the cation at the six-membered ring (MCHA(I)) and the other with the cation at the 8-membered ring (MCHA(IV)). The O(2)-HCHA and O(2)-NaCHA adsorption complexes present a eta(1)-O(2) bent coordination. The adsorption energies, which are due to dispersion, are between -15 and -19 kJ mol(-1), in agreement with the experimental values. On the other hand, the O(2) coordination to CuCHA is through a eta(2)-side-on mode with a square planar coordination around the metal center. This structure favors the Cu d -->pi* O(2) charge transfer which becomes the predominant stabilizing factor. The adsorption of singlet states of O(2) in HCHA and NaCHA, modeled with an ONIOM M12T:48T, is of the same nature as that of the ground state, and only the highest in energy (1)Sigma is significantly more stabilized in MCHA than the triplet state by 14 to 24 kJ mol(-1). The adsorption of singlet O(2) in Cu exchanged zeolites presents a higher electron transfer from Cu(+) to O(2) than that calculated for the triplet species and thus both singlet states are stabilized with respect to the ground state O(2). Generally, singlet oxygen appears more attractive to active zeolite models than those calculated with triplet oxygen, indicating a source of oxidative efficiency for designed structures.