Physical Chemistry The Chemical Bond

Computational biochemistry

Topic overview

Start with the big picture

The lesson begins with the Born–Oppenheimer approximation, which separates nuclear and electronic motion to make electronic-structure calculations practical. It compares ab initio methods, including Hartree–Fock and post-Hartree–Fock approaches, with density functional theory, and explains how basis-set choice affects accuracy and computational cost. Molecular mechanics force fields describe atoms through bonded and non-bonded interactions, with reliability shaped by parameterization and transferability. The topic then turns to molecular dynamics, Monte Carlo sampling, enhanced-sampling techniques, and free-energy methods, noting that convergence and entropy can remain challenging. Finally, it introduces QM/MM modeling, which treats a reactive region quantum mechanically and its surroundings with molecular mechanics.

Learning objectives

What you'll learn

  • Explain how the Born–Oppenheimer approximation simplifies electronic-structure calculations.
  • Distinguish ab initio methods, density functional theory, and molecular mechanics.
  • Describe how basis sets and force-field parameterization influence model accuracy and cost.
  • Compare molecular dynamics, Monte Carlo, and enhanced-sampling approaches.
  • Explain the purpose of free-energy methods and QM/MM modeling.
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