About this book Computational Chemistry Using the PC, Third Edition takes the reader from a basic mathematical foundation to beginning research-level calculations, avoiding expensive or elaborate software in favor of PC applications. Geared towards an advanced undergraduate or introductory graduate course, this Third Edition has revised and expanded coverage of molecular mechanics, molecular orbital theory, molecular quantum chemistry, and semi-empirical and ab initio molecular orbital approaches.

With significant changes made to adjust for improved technology and increased computer literacy, Computational Chemistry Using the PC, Third Edition gives its readers the tools they need to translate theoretical principles into real computational problems, then proceed to a computed solution. Students of computational chemistry, as well as professionals interested in updating their skills in this fast-moving field, will find this book to be an invaluable resource. Reviews "…includes a wealth of computer projects, exercises…and problems to challenge any group of sharp, industrious students.

For forty years, Professor Rogers has taught academic courses in physical chemistry, thermodynamics, general chemistry, computational chemistry, and microcomputer interfacing. He publishes regularly in the Journal of Physical Chemistry and elsewhere, and his work has been supported for the last decade by the National Science Foundation through the National Center for Supercomputing Applications. Export Citation s. Export Citation. Plain Text. Reviews "…includes a wealth of computer projects, exercises…and problems to challenge any group of sharp, industrious students.

For forty years, Professor Rogers has taught academic courses in physical chemistry, thermodynamics, general chemistry, computational chemistry, and microcomputer interfacing. He publishes regularly in the Journal of Physical Chemistry and elsewhere, and his work has been supported for the last decade by the National Science Foundation through the National Center for Supercomputing Applications.

Free Access. Summary PDF Request permissions. Tools Get online access For authors. Email or Customer ID. Forgot password? Old Password. New Password. For very large systems, the relative total energies can be compared using molecular mechanics. The ways of determining the total energy to predict molecular structures are:. This does not imply that the solution is an exact one; they are all approximate quantum mechanical calculations.

It means that a particular approximation is rigorously defined on first principles quantum theory and then solved within an error margin that is qualitatively known beforehand. The simplest type of ab initio electronic structure calculation is the Hartree—Fock method HF , an extension of molecular orbital theory , in which the correlated electron-electron repulsion is not specifically taken into account; only its average effect is included in the calculation.

As the basis set size is increased, the energy and wave function tend towards a limit called the Hartree—Fock limit. Many types of calculations termed post-Hartree—Fock methods begin with a Hartree—Fock calculation and subsequently correct for electron-electron repulsion, referred to also as electronic correlation. To obtain exact agreement with experiment, it is necessary to include relativistic and spin orbit terms, both of which are far more important for heavy atoms.

In all of these approaches, along with choice of method, it is necessary to choose a basis set. This is a set of functions, usually centered on the different atoms in the molecule, which are used to expand the molecular orbitals with the linear combination of atomic orbitals LCAO molecular orbital method ansatz.

## Journal of Computational Chemistry, Volume 22

Ab initio methods need to define a level of theory the method and a basis set. The Hartree—Fock wave function is a single configuration or determinant. In some cases, particularly for bond breaking processes, this is inadequate, and several configurations must be used. Here, the coefficients of the configurations, and of the basis functions, are optimized together. The total molecular energy can be evaluated as a function of the molecular geometry ; in other words, the potential energy surface.

Such a surface can be used for reaction dynamics. The stationary points of the surface lead to predictions of different isomers and the transition structures for conversion between isomers, but these can be determined without a full knowledge of the complete surface. A particularly important objective, called computational thermochemistry , is to calculate thermochemical quantities such as the enthalpy of formation to chemical accuracy. To reach that accuracy in an economic way it is necessary to use a series of post-Hartree—Fock methods and combine the results.

These methods are called quantum chemistry composite methods. Density functional theory DFT methods are often considered to be ab initio methods for determining the molecular electronic structure, even though many of the most common functionals use parameters derived from empirical data, or from more complex calculations.

In DFT, the total energy is expressed in terms of the total one- electron density rather than the wave function. In this type of calculation, there is an approximate Hamiltonian and an approximate expression for the total electron density. DFT methods can be very accurate for little computational cost.

Linear Nonhomogeneous Simultaneous Equations. Matrix Inversion and Diagonalization. Chapter 3.

### Services on Demand

Curve Fitting. Information Loss.

The Method of Least Squares. Least Squares Minimization. Linear Functions Passing Through the Origin. Quadratic Functions. Polynomials of Higher Degree. Statistical Criteria for Curve Fitting. Reliability of Fitted Parameters. Reliability of Fitted Polynomial Parameters. Multivariate Least Squares Analysis.

Error Analysis.

## Computational Chemistry Using the PC

Chapter 4. Molecular Mechanics: Basic Theory. The Harmonic Oscillator. The Two-Mass Problem. Polyatomic Molecules. Molecular Mechanics. Ethylene: A Trial Run. The Geo File. The Output File. The GUI Interface. The Energy Equation. Sums in the Energy Equation: Modes of Motion.

Cross Terms. Chapter 5. Molecular Mechanics II: Applications. Normal Coordinates. Normal Modes of Motion. The Hessian Matrix. The Enthalpy of Formation.