Quantum chemistry is the branch of chemistry that applies the principles of quantum mechanics (wave functions, Schrödinger equation, orbitals, etc.) to understand how atoms and molecules behave.
In computational chemistry, scientists use mathematical models and computer programs to simulate chemical systems. Quantum chemistry forms the foundation for this because chemical bonding, molecular structure, and reactions are all governed by quantum rules.
Here’s how quantum chemistry is used in computational chemistry:
- Predicting molecular structure
- Using quantum mechanics, computers can calculate the most stable arrangement of atoms in a molecule.
- For example: predicting bond lengths, bond angles, and 3D shapes.
- Calculating energies
- Quantum chemistry helps compute total energy, binding energy, and reaction energies.
- This is important for predicting whether a reaction will happen or not.
- Modeling electron behavior
- Electrons can’t be described by classical physics. Quantum chemistry models their probability distribution (orbitals, electron density).
- This helps explain chemical bonding and reactivity.
- Studying chemical reactions
- Computational chemists use quantum chemistry to simulate reaction pathways, transition states, and activation energies.
- This shows how fast and how easily reactions occur.
- Spectroscopy and properties
- Quantum calculations predict IR, UV-Vis, NMR spectra, and other molecular properties.
- This helps compare theory with experimental data.
- Drug design and materials science
- Quantum chemistry-based simulations help in designing new drugs, catalysts, nanomaterials, and even batteries by predicting how molecules interact before doing expensive lab experiments.
In short:
Quantum chemistry provides the rules, and computational chemistry applies those rules with computers to predict and simulate real chemical systems.