Quantum Chemistry - Molecules for Innovations

212 Pages·2012·7.869 MB·English

by  T. Tada

QUANTUM CHEMISTRY –
MOLECULES FOR
INNOVATIONS

Edited by Tomofumi Tada
Quantum Chemistry – Molecules for Innovations
Edited by Tomofumi Tada

Published by InTech
Janeza Trdine 9, 51000 Rijeka, Croatia

Copyright © 2012 InTech
All chapters are Open Access distributed under the Creative Commons Attribution 3.0
license, which allows users to download, copy and build upon published articles even for
commercial purposes, as long as the author and publisher are properly credited, which
ensures maximum dissemination and a wider impact of our publications. After this work
has been published by InTech, authors have the right to republish it, in whole or part, in
any publication of which they are the author, and to make other personal use of the
work. Any republication, referencing or personal use of the work must explicitly identify
the original source.

As for readers, this license allows users to download, copy and build upon published
chapters even for commercial purposes, as long as the author and publisher are properly
credited, which ensures maximum dissemination and a wider impact of our publications.

Notice
Statements and opinions expressed in the chapters are these of the individual contributors
and not necessarily those of the editors or publisher. No responsibility is accepted for the
accuracy of information contained in the published chapters. The publisher assumes no
responsibility for any damage or injury to persons or property arising out of the use of any
materials, instructions, methods or ideas contained in the book.

Publishing Process Manager Sasa Leporic
Technical Editor Teodora Smiljanic
Cover Designer InTech Design Team

First published March, 2012
Printed in Croatia

A free online edition of this book is available at www.intechopen.com
Additional hard copies can be obtained from [email protected]

Quantum Chemistry – Molecules for Innovations, Edited by Tomofumi Tada
p. cm.
ISBN 978-953-51-0372-1

Contents

Preface IX
Part 1 Theories in Quantum Chemistry 1
Chapter 1 Numerical Solution of Linear
Ordinary Differential Equations in
Quantum Chemistry by Spectral Method 3
Masoud Saravi and Seyedeh-Razieh Mirrajei
Chapter 2 Composite Method Employing
Pseudopotential at CCSD(T) Level 11
Nelson Henrique Morgon
Part 2 Electronic Structures and Molecular Properties 23
Chapter 3 Quantum Chemical Calculations
for some Isatin Thiosemicarbazones 25
Fatma Kandemirli, M. Iqbal Choudhary,
Sadia Siddiq, Murat Saracoglu, Hakan Sayiner,
Taner Arslan, Ayşe Erbay and Baybars Köksoy
Chapter 4 Elementary Molecular Mechanisms of
the Spontaneous Point Mutations in DNA:
A Novel Quantum-Chemical Insight into
the Classical Understanding 59
O.O. Brovarets’, I.M. Kolomiets’ and D.M. Hovorun
Chapter 5 Quantum Chemistry and Chemometrics
Applied to Conformational Analysis 103
Aline Thaís Bruni and Vitor Barbanti Pereira Leite
Part 3 Molecules to Nanodevices 131
Chapter 6 Quantum Transport and Quantum Information
Processing in Single Molecular Junctions 133
Tomofumi Tada
VI Contents

Chapter 7 Charge Carrier Mobility in Phthalocyanines:
Experiment and Quantum Chemical Calculations 159
Irena Kratochvilova
Chapter 8 Theoretical Study for High Energy
Density Compounds from Cyclophosphazene 175
Kun Wang, Jian-Guo Zhang, Hui-Hui Zheng,
Hui-Sheng Huang and Tong-Lai Zhang

Preface

Molecules, small structures composed of atoms, are essential substances for lives.
However, we didn’t have the clear answer to the following questions until the 1920s:
why molecules can exist in stable as rigid networks between atoms, and why
molecules can change into different types of molecules. The most important event for
solving the puzzles is the discovery of the quantum mechanics. Quantum mechanics is
the theory for small particles such as electrons and nuclei, and was applied to
hydrogen molecule by Heitler and London at 1927. The pioneering work led to the
clear explanation of the chemical bonding between the hydrogen atoms. This is the
beginning of the quantum chemistry. Since then, quantum chemistry has been an
important theory for the understanding of molecular properties such as stability,
reactivity, and applicability for devices.
Quantum chemistry has now two main styles: (i) the precise picture (computations)
and (ii) simple picture (modeling) for describing molecular properties. Since the
Schrodinger equation, the key differential equation in quantum mechanics, cannot be
solved for polyatomic molecules in the original many-body form, some
approximations are required to apply the equation to molecules. A popular strategy is
the approximation of the many-body wave functions by using single-particle wave
functions in a single configuration. The single-particle wave function can be
represented with the linear combination of atomic orbitals (LCAOs), and the
differential equation to be solved is consequently converted to a matrix form, in which
matrices are written in AO basis. This strategy immediately leads to the Hartree-Fock
Roothaan equation, and this is an important branching point toward the precise
computations or appropriate modeling. Since the approximations made in the Hartree-
Fock Roothaan equation can be clearly recognized, the descriptions of many-body
wave functions are expected to be better and better by using much more AOs, multi-
configurations, and more rigorous treatment for many-body interactions. Prof. J. A.
Pople was awarded the Novel prize in Chemistry at 1998 for his pioneering works
devoted for the development of the wave function theory toward the precise picture of
molecular properties. The style is of course quite important, especially when we
roughly know what are the interesting properties in a target molecule, because our
efforts in those cases must be made to obtain more quantitative description of the
target properties. However, when we don’t know what the interesting properties of
X Preface

the target molecule are, we have to take care whether a quantum chemical method in
your hand is really appropriate for your purpose because an expensive method using
many AOs and configurations sometimes falls into a difficulty in the extraction of the
intrinsic property of the target molecule. Thus, we have to turn to the second style, the
simple picture, to capture the properties of the target molecule roughly. For example, a
simple π orbital picture is useful to predict the reactivity of π organic molecules on the
basis of the frontier orbital theory in which the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) are the key orbitals for the
prediction of the chemical response of the target molecule. When symbolized AOs (i.e.,
AOs represented neither in analytical nor in numerical form) are adopted for
calculations, the Hamiltonian matrix is simply represented only with the numbers “0”
and “1”. Despite the simple description for the molecule, the frontier orbitals
calculated (sometimes by hand) from the Hamiltonian are quite effective for the
prediction of the reactivity of the target molecule. Prof. K. Fukui, the pioneer of the
frontier orbital theory, was awarded the Novel prize in Chemistry at 1981.
Nowadays, our target molecules are structured as more diverse atomic networks and
embedded in more complicated environment. The molecular properties are thus
inevitably dependent on the complicated situations, and therefore we need the
balanced combination of both styles, simple-and-precise picture, for the target today.
We have to consider how we should build the veiled third style. To keep this in mind,
this book is composed of nine chapters for the quantum chemical theory, conventional
applications and advanced applications. I sincerely apologize this book cannot cover
the broad spectrum of quantum chemistry. However, I hope this book, Quantum
Chemistry – Molecules for Innovation, will be a hint for younger generations.

Tomofumi Tada
Global COE for Mechanical Systems Innovation,
Department of Materials Engineering, The University of Tokyo,
Japan