Jesús Sánchez-Márquez

Introducing “UCA-FUKUI” software: reactivity-index calculations

A new software (UCA-FUKUI) has been developed to facilitate the theoretical study of chemical reactivity. This program can calculate global parameters like hardness, softness, philicities, and Fukui condensed functions, and also local parameters from the condensed functions. To facilitate access to the program we have developed a very easy-to-use interface. We have tested the performance of the software by calculating the global and local reactivity indexes of a group of representative molecules. Finite difference and frontier molecular orbital methods were compared and their correlation tested. Finally, we have extended the analysis to a set of ligands of importance in coordination chemistry, and the results are compared with the exact calculation. As a general trend, our study shows the existence of a high correlation between global parameters, but a weaker correlation between local parameters.

Convergent study of Ru–ligand interactions through QTAIM, ELF, NBO molecular descriptors and TDDFT analysis of organometallic dyes

We report a theoretical study of a series of Ru complexes of interest in dye-sensitised solar cells, in organic light-emitting diodes, and in the war against cancer. Other metal centres, such as Cr, Co, Ni, Rh, Pd, and Pt, have been included for comparison purposes. The metal–ligand trends in organometallic chemistry for those compounds are shown synergistically by using three molecular descriptors: quantum theory of atoms in molecules (QTAIM), electron localisation function (ELF) and second-order perturbation theory analysis of the natural bond orbital (NBO). The metal–ligand bond order is addressed through both delocalisation index (DI) of QTAIM and fluctuation index (λ) of ELF. Correlation between DI and λ for Ru–N bond in those complexes is introduced for the first time. Electron transfer and stability was also assessed by the second-order perturbation theory analysis of the NBO. Electron transfer from the lone pair NBO of the ligands toward the antibonding lone pair NBO of the metal plays a relevant role in stabilising the complexes, providing useful insights into understanding the effect of the ‘expanded ligand’ principle in supramolecular chemistry. Finally, absorption wavelengths associated to the metal-to-ligand charge transfer transitions and the highest occupied molecular orbital (HOMO)--lowest unoccupied molecular orbital (LUMO) characteristics were studied by time-dependent density functional theory.

Reactivity indices for natural bond orbitals: a new methodology

A new reactivity index has been defined; this parameter is focused on a molecule’s natural bond orbitals (NBOs) and derives in a natural way from Fukui functions. NBOs have the advantage of being very localized, allowing the reaction site of an electrophile or nucleophile to be determined within a very precise molecular region. Finally, the indices for a representative set of organic molecules were calculated and their usefulness tested on some protonation reactions.

Introducing a new bond reactivity index: Philicities for natural bond orbitals

AbstractIn the present work, a new methodology defined for obtaining reactivity indices (philicities) is proposed. This is based on reactivity functions such as the Fukui function or the dual descriptor, and makes it possible to project the information from reactivity functions onto molecular orbitals, instead of onto the atoms of the molecule (atomic reactivity indices). The methodology focuses on the molecules’ natural bond orbitals (bond reactivity indices) because these orbitals have the advantage of being localized, allowing the reaction site of an electrophile or nucleophile to be determined within a very precise molecular region. This methodology provides a “philicity” index for every NBO, and a representative set of molecules has been used to test the new definition. A new methodology has also been developed to compare the “finite difference” and the “frontier molecular orbital” approximations. To facilitate their use, the proposed methodology as well as the possibility of calculating the new indices have been implemented in a new version of UCA-FUKUI software. In addition, condensation schemes based on atomic populations of the “atoms in molecules” theory, the Hirshfeld population analysis, the approximation of Mulliken (with a minimal basis set) and electrostatic potential-derived charges have also been implemented, including the calculation of “bond reactivity indices” defined in previous studies. Graphical abstractA new methodology defined for obtaining bond reactivity indices (philicities) is proposed and makes it possible to project the information from reactivity functions onto molecular orbitals. The proposed methodology as well as the possibility of calculating the new indices have been implemented in a new version of UCA-FUKUI software. In addition, this version can use new atomic condensation schemes and new “utilities” have also been included in this second version.

Software to obtain accurate Gaussian expansions for a wide range of radial functions

is easy to achieve when the exponents βi are assumed to be known, but it is very difficult to realize [1–3] when the values of these exponents must be optimized. The optimization of the exponents is often important, since it leads to a good representation of F(r) with a moderate number of Gaussian functions. This kind of development is useful in the field of quantum chemistry [1–4], as it enables the polycentric integrals

Introducing a new methodology for the calculation of local philicity and multiphilic descriptor: an alternative to the finite difference approximation

ABSTRACT This work presents a new development based on the condensation scheme proposed by Chamorro and Pérez, in which new terms to correct the frozen molecular orbital approximation have been introduced (improved frontier molecular orbital approximation). The changes performed on the original development allow taking into account the orbital relaxation effects, providing equivalent results to those achieved by the finite difference approximation and leading also to a methodology with great advantages. Local reactivity indices based on this new development have been obtained for a sample set of molecules and they have been compared with those indices based on the frontier molecular orbital and finite difference approximations. A new definition based on the improved frontier molecular orbital methodology for the dual descriptor index is also shown. In addition, taking advantage of the characteristics of the definitions obtained with the new condensation scheme, the descriptor local philicity is analysed by separating the components corresponding to the frontier molecular orbital approximation and orbital relaxation effects, analysing also the local parameter multiphilic descriptor in the same way. Finally, the effect of using the basis set is studied and calculations using DFT, CI and Möller–Plesset methodologies are performed to analyse the consequence of different electronic-correlation levels.

Simplified box orbitals for molecules containing atoms beyond Ar

ABSTRACT Simplified Box Orbitals (SBOs) are a kind of spatially restricted basis functions with a similar use to Slater functions, but fulfilling an exact version of the zero-differential overlap approximation. These functions also allow for a drastic reduction in the number of bielectronic integrals when dealing with huge systems, and can be adapted to study confined systems such as molecules in solution. In previous studies, the necessary SBOs parameters to be used for different elements were defined. However, the accuracy of those basis functions decreases with the atomic number of the atoms under study, and therefore their use was discouraged beyond the Ar atom. In the present study, we verify that slightly increasing the terms of SBOs for a better definition, is enough to correctly handling atoms beyond Ar. This, together with other improvements exposed in this work, allowed obtaining accurate SBOs for K–Kr atoms. To make possible the use of SBOs in standard quantum chemistry calculation software, Gaussian expansions to the proposed basis functions–were achieved. Then, simple formulas for directly obtaining those expansions were deduced. Finally, the results of an SZ basis set of the proposed SBOs are analysed and compared with a similar STO basis set. GRAPHICAL ABSTRACT