kvantkeemias

Quantum chemistry, or kvantkeemia in Estonian, is the branch of chemistry that uses quantum mechanics to investigate the structure, properties, and reactions of atoms and molecules. It seeks to predict molecular energies, geometries, vibrational frequencies, and spectra from first principles, often without empirical parameters.

The core task is solving the electronic Schrödinger equation for molecules under the Born–Oppenheimer approximation, which treats nuclei as fixed while electrons move. This yields potential energy surfaces that govern chemical reactivity and molecular dynamics.

Computational methods span ab initio approaches such as Hartree–Fock and post-Hartree–Fock methods (MP2, CCSD(T)); density functional theory (DFT) with exchange-correlation functionals; and semi-empirical methods that trade accuracy for speed. Calculations use basis sets to represent electronic wavefunctions. Time-dependent extensions (TD-DFT) enable excited-state properties. For large systems, QM/MM hybrids combine quantum treatment of a reactive region with classical models of the surroundings.

Applications include predicting molecular geometries and reaction mechanisms, interpreting and predicting spectra, studying catalysis, materials properties, and drug design. The field underpins much of computational chemistry, materials science, and chemical physics, and is closely tied to experimental spectroscopy and thermodynamics.

Challenges include balancing accuracy and computational cost, limitations of approximate functionals, difficulties with strongly correlated systems, and the treatment of excited states and nonadiabatic effects. Ongoing developments in more accurate functionals, multi-reference methods, and scalable algorithms aim to extend reach to larger, more complex systems.