Reactividad química en el contexto de la teoría de los funcionales de la densidad
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Fecha
2007
Autores
Profesor/a Guía
Facultad/escuela
Idioma
es
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Universidad Andrés Bello
Nombre de Curso
Licencia CC
Licencia CC
Resumen
La teoría de los funcionales de la densidad (DFT) establece un marco en donde construir
una teoría de reactividad química simple, transparente y que guarda relación directa con
conceptos empíricos de la química. La reactividad química es la respuesta de un sistema
molecular frente a diferentes perturbaciones. En DFT, esta respuesta es caracterizada
mediante descriptores de reactividad química que constituyen los coeficientes de una
expansión en series de Taylor de una perturbación del estado fundamental de los reactivos.
Esta perturbación puede afectar cualquiera de las variables fundamentales del sistema y la
respuesta del sistema puede ser tanto electrónica como en las posiciones nucleares. Tales
respuestas constituyen en sí mismas los así llamados esquemas de reactividad electrónica y
nuclear, respectivamente.
En esta tesis se extendió el formalismo de reactividad nuclear al caso de polarización de
espín, con el fin de incluir todos los efectos de espín en la respuesta nuclear. También se
construyó un método preciso para evaluar la función nuclear de Fukui y cualquier índice
definido en· términos de una derivada respecto al número de electrones. Los métodos
aproximados más comunes usados para evaluar la función nuclear de Fukui fueron
contrastados con el nuevo esquema de cálculo.
Por otro lado, se desarrollo y exploró la utilidad de un esquema de reactividad química
descrito en el marco del formalismo de Kohn y Sham, en el cual muchas de las
aproximaciones usadas para evaluar los índices estándar de reactividad son exactas. De esta
manera, se establecieron las bases fisicas sobre las que se fundamentan estas
aproximaciones, lo cual permite entender mejor los límites de los modelos teóricos que
soportan.
Finalmente, este trabajo de tesis abordó el desarrollo y aplicación de modelos de
reactividad adecuados para explorar los patrones locales de reactividad en sistemas
extendidos. Estos modelos se construyeron a partir de la densidad de estados, la cual es un
resultado estándar de un cálculo ab initio. Estos modelos fueron aplicados exitosamente en
la racionalización de la naturaleza reactiva de ciertos nanotubos de carbono y superficies de
óxidos alcalinotérreos.
Density functional theory (DFT) establishes a useful theoretical framework to build a theory of chemical reactivity intimately related with empirical concepts of chemistry. Chemical reactivity is the response of system against a perturbation. Within the context of DFT this response is represented by descriptors corresponding to the coefficients of an expansion in Taylor's series of a perturbation of the ground state of the reactants. This perturbation can affect any ofthe system's fundamental variables, and the responses can be both electronic and in nuclei positions. Such a responses itself constitutes the so-called electronic and nuclear reactivity frameworks, respectively. In this thesis, the scheme of nuclear reactivity was extended to the spin polarized case in order to include the spin effects in the nuclear response. We also developed a precise method to evaluate the nuclear Fukui function and any reactivity index defined in terms of a derivative with respect to the number of electrons. Other common methods used to compute the nuclear Fukui function were contrasted against our proposal. On the other hand, we have developed and explored the usefulness of a reactivity scheme defined within the context of the Kohn and Sham formalism. Many of the standard approximations commonly used to evaluated chemical reactivity descriptors are exact in this scheme. In this way, we contribute to the establishment of physical grounds for these approximations, which allow us to improve our comprehension and the limits of theoretical models based on it.. Finally, this thesis work focused on the development and application of chemical reactivity models intended to be suitable to describe the pattems of local reactivity in extended systems. These models were constructed on the basis of local density of states, a standard result of any ab initio calculation. These models were successfully applied here to the rationalization of the reactive nature of sorne carbon nanotubes and alkaline earth oxides surfaces.
Density functional theory (DFT) establishes a useful theoretical framework to build a theory of chemical reactivity intimately related with empirical concepts of chemistry. Chemical reactivity is the response of system against a perturbation. Within the context of DFT this response is represented by descriptors corresponding to the coefficients of an expansion in Taylor's series of a perturbation of the ground state of the reactants. This perturbation can affect any ofthe system's fundamental variables, and the responses can be both electronic and in nuclei positions. Such a responses itself constitutes the so-called electronic and nuclear reactivity frameworks, respectively. In this thesis, the scheme of nuclear reactivity was extended to the spin polarized case in order to include the spin effects in the nuclear response. We also developed a precise method to evaluate the nuclear Fukui function and any reactivity index defined in terms of a derivative with respect to the number of electrons. Other common methods used to compute the nuclear Fukui function were contrasted against our proposal. On the other hand, we have developed and explored the usefulness of a reactivity scheme defined within the context of the Kohn and Sham formalism. Many of the standard approximations commonly used to evaluated chemical reactivity descriptors are exact in this scheme. In this way, we contribute to the establishment of physical grounds for these approximations, which allow us to improve our comprehension and the limits of theoretical models based on it.. Finally, this thesis work focused on the development and application of chemical reactivity models intended to be suitable to describe the pattems of local reactivity in extended systems. These models were constructed on the basis of local density of states, a standard result of any ab initio calculation. These models were successfully applied here to the rationalization of the reactive nature of sorne carbon nanotubes and alkaline earth oxides surfaces.
Notas
Tesis (Doctor en Fisicoquímica Molecular)
Palabras clave
Funciones de Densidad, Reactividad (Química), Fisicoquímica Molecular