There are many fine scripts of quantum chemistry and physics in print at this time. So the question can be raised as to why we would write another script, especially one focusing on the smaller discipline of quantum chemistry. When we began this project years ago, we felt that we were a unique juncture in quantum chemistry and technology and that, immodestly, we had a unique perspective to offer to students.

Much of the mainstream of quantum chemistry is now deeply tied to quantum physics, in a cooperative endeavor called “quantum science.” At the same time, there is a large, growing, and vital community of people who use the applications of quantum chemistry to tackle wide-ranging set of problems in the biological, physical and environmental sciences, engineering, medicine and so on.

We thought it was important to bring together, in a single volume, a rigorous, detailed perspective on both the “pure” and “applied” aspects of quantum chemistry. As such, one might find more detail about any particular subject than one might like. We hope this encourages instructors to summarize the script material and present it in a manner most suitable to a particular audience. The amount of material contained in this book is too much for a one quarter or one semester course and a bit too little for a yearlong course. Instructors can pick and choose which material seems most suitable for their course.