Quantum mechanical treatments, chemical acids

The early chapters in this book deal with chemical reactions. Stoichiometry is covered in Chapters 3 and 4, with special emphasis on reactions in aqueous solutions. The properties of gases are treated in Chapter 5, followed by coverage of gas phase equilibria in Chapter 6. Acid-base equilibria are covered in Chapter 7, and Chapter 8 deals with additional aqueous equilibria. Thermodynamics is covered in two chapters Chapter 9 deals with thermochemistry and the first law of thermodynamics Chapter 10 treats the topics associated with the second law of thermodynamics. The discussion of electrochemistry follows in Chapter 11. Atomic theory and quantum mechanics are covered in Chapter 12, followed by two chapters on chemical bonding and modern spectroscopy (Chapters 13 and 14). Chemical kinetics is discussed in Chapter 15, followed by coverage of solids and liquids in Chapter 16, and the physical properties of solutions in Chapter 17. A systematic treatment of the descriptive chemistry of the representative elements is given in Chapters 18 and 19, and of the transition metals in Chapter 20. Chapter 21 covers topics in nuclear chemistry and Chapter 22 provides an introduction to organic chemistry and to the most important biomolecules. 

The most fundamental level of modeling of any chemical system employs quantum mechanics. Quantum mechanical (QM) treatments are required to understand many important chemical and biological properties of nucleic acids. Moreover, empirical force-field methods, employed to study the conformations of polynucleotides, rely on quantum calculations to obtain crucial parameters that are difficult to measure experimentally, such as atom-centered charges for calculating electrostatic interactions. The obtain a description of a chemical system using QM one solves the time-independent Schrodinger equation with or without the use of empirical parameters. 

An alternative approach is to combine QM and MM methods such that the reacting system (or the active site in an enzyme) is treated explicitly by a quantum mechanical method, while the surrounding environmental solvent molecules (or amino acids), which constitute the most time-consuming part in the evaluation of the potential energy surface, are approximated by a standard MM force field. " Such a method takes advantage of the accuracy and generality of the QM treatment for chemical reactions - and of the computational efficiency of the MM calculation.Because the reactant electronic structure and solute-solvent interactions are determined quantum mechanically, the procedure is appropriate for studying chemical reactions, and there is no need to parameterize potential functions for every new reaction. Furthermore, the solvent polarization effects on the solute are naturally included in the... 

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