Ficha Cuerpo Académico
Esp
Development and applications of density functional theory
Discipline Physical chemistry
Academic Group Consolidated
Year of registration: 2005
Members
Knowledge Generation and Application Lines
1.- Development and application of chemical reactivity parameters.
2.- Description of chemical systems stabilized by hydrogen bridges.
3.- Design of heavy metal selective binders.
4.- Study of the effects of the substituent on the chemical reactivity of organic molecules.
5.- Electronic structure of biomolecules.
6.- Electronic structure of systems under pressure.
Description
1.- Density functional theory has made it possible to formalize some empirical reactivity parameters and to define new ones. In general, these properties are related to some derivatives of the energy. Within this line, a general method was developed to determine variationally, in molecular systems, two of these quantities: the Fukui function and the hardness. This method is being implemented in a Hückel-type approximation to test its predictive capacity. The maximum hardness principle was also analyzed by introducing an electronic system in a large canonical ensemble; in this case some stabil...
Read more
1.- Density functional theory has made it possible to formalize some empirical reactivity parameters and to define new ones. In general, these properties are related to some derivatives of the energy. Within this line, a general method was developed to determine variationally, in molecular systems, two of these quantities: the Fukui function and the hardness. This method is being implemented in a Hückel-type approximation to test its predictive capacity. The maximum hardness principle was also analyzed by introducing an electronic system in a large canonical ensemble; in this case some stability zones were found and validity conditions for this principle were obtained. Additionally, these reactivity parameters were applied to try to understand the bond breaking processes in symmetrical organic molecules; this study is still under development and a method to determine some reactivity criteria for species in solution is being sought.
2.- It is undoubtedly recognized nowadays that the inter and intramolecular contacts by hydrogen bridges are important in the stabilization of many chemical systems. This academic body has studied the scope and limitations of some methods of quantum chemistry for the description of systems showing hydrogen bridge bonds. In particular, the results obtained by the Kohn-Sham method and the second order perturbation theory method, MP2, have been contrasted. This comparison is important since the Kohn-Sham model, due to the way it was designed, consumes less computational time and therefore generates faster results with respect to the MP2 method. However, the Kohn-Sham method fails to predict weak force hydrogen bridge contacts. In order to have a reliable comparison, currently this academic body has direct interaction with two experimental groups, one in electrochemistry at the Universidad Autónoma Metropolitana Unidad Iztapalapa and the other in the chemistry department of UPIBI of the Instituto Politécnico Nacional (National Polytechnic Institute). There is also close collaboration with the Pacific Northwest National Laboratory and the Oak Ridge National Laboratory in the United States of America. Experimental groups are trying to use magnetic properties of matter, such as the shielding constant that appears in NMR or the coupling constant that is involved in EPR. In addition, different solvent models are being evaluated to see what is the effect on hydrogen bridges.
3.- The interaction of metal ions with organic molecules has a relevant role in the design of selective multidentate binders of metals that are recognized as pollutants and harmful to health. This interaction can be modeled by making use of force fields in order to apply to large systems. Recently, ab initio methods have been used as a reliable source of geometrical and energetic parameters that are necessary for force fields. In particular, the Density Functional Theory (DFT) is a method that, due to its lower computational cost, becomes a good option for the generation of these parameters. In this line of knowledge generation, DFT is used for the characterization of the interactions between metals and binders in order to model these interactions in a force field. The aim of these studies is to control the selectivity of the ligand for the metal ion by manipulating the denticity; in this direction there is a close collaboration with Dr. Benjamin P. Hay of the Pacific Northwest National Laboratory, since he has experience in the parameterization of interactions in metal complexes. There are also metal complexes that fluoresce; this property has been used in the in situ detection of heavy metals. A large number of ligands with this property have been found experimentally, although it is not yet fully understood how the interactions of the ligand with the metal increase or induce fluorescence. In this line, time-dependent PDT will be used to study the fluorescent properties of selective ligands that complex heavy metals.
4.- The prediction of the properties of new molecules and in particular of their reactivity is one of the main objectives of chemistry. In this project the effect that generates the change of a substituent in different families of organic molecules is analyzed; Since each family of compounds presents a characteristic behavior, it is necessary to use different descriptors for each case, and even to define new parameters; The orienting effect in monosubstituted benzenes, the variation of the electrophilicity of the carbonyl group, the acidity of benzoic and acetic acids, and the activity of some free radical generators will be studied. In the case of substituted benzenes a multideterminant description of the wave function of the system is required; for this reason CASSCF type calculations will be performed. For the study of carbonyls a local extension of the new electrophilicity index based on the application of the variational principle of the Fukui function will be proposed. The description of the acidity of organic molecules requires the construction of a fragment model for the protonation process. This model will allow relating some microscopic properties with the protonation energy. Finally, a model will be developed to apply the spin-dependent extension of density functional theory to the problem of free radical generation in peroxides and diazenes. The application of the theory to these systems and the construction of reactivity models will help to understand the role of substituent characteristics in different chemical environments and their effect on the electronic properties of the molecules.
5.- Knowledge of the electronic structure of any system allows us to understand details of its nature that cannot be studied without including the quantum behavior of the electrons. Among these "quantum facets" of the systems, chemical rectivity stands out. Understanding this part of the behavior of systems involves not only rationalizing kinetic constants, but also elucidating the effects that control selectivity and activation by external perturbations. Another topic that requires knowledge of electronic structure is that of intermolecular interactions in general. For a long time, studies of the electronic structure of biomolecules were restricted to models whose sizes precluded consideration of cooperative effects. It is now known that these effects play a very relevant role in understanding the chemical reactivity and intermolecular interactions of biomolecules. In fact, it is common that realistic models for understanding the biological function of macromolecules are of one dimension in the nanoscale range. The interest of this LGAC is focused on the application of all methodological tools, developed within the context of Density Functional Theory, to the study of the electronic structure of biomolecules. The emphasis of this LGAC is placed on the understanding of the cooperative effects, of diverse nature, that occur at the nanoscale and that give biomolecules their functional characteristics.
6.- The study of atoms and molecules under pressure is of great interest, since at the bottom of the earth and in the formation of stars, matter is found in extreme situations. It is to be expected that under such conditions the chemical behavior of atoms and molecules will be different from the chemistry we observe on the surface of our planet. For this reason, attempts have long been made to simulate both experimentally and theoretically the effect of pressure on matter. In this academic body, the model of electronic systems confined by impenetrable walls has been used to simulate the effect of pressure on atomic systems; currently, alternative numerical methods are being implemented for the study of molecules confined by rigid walls, making use of the methods of quantum chemistry. The intention is to analyze the breaking or formation of chemical bonds by the effect of confinement and to contrast with the chemistry that we observe in non-extreme situations. In this line of research we have had direct collaboration with Dr. Norberto Aquino of the Department of Physics of the Universidad Autónoma Metropolitana Unidad Iztapalapa and Dr. Kalidas Sen of the University of Hyderabad in India.
Return to list
