Kvantkeemiat

Kvantkeemiat, or quantum chemistry, is the branch of chemistry that uses the principles and tools of quantum mechanics to study the electronic structure of atoms, molecules, and extended systems. Its central aim is to explain chemical bonding, predict molecular properties, and illuminate reaction mechanisms by solving or approximating solutions to the electronic Schrödinger equation under appropriate approximations such as the Born–Oppenheimer approximation.

The field relies on a range of theoretical methods. Ab initio approaches, including Hartree–Fock theory and post–Hartree–Fock methods (such as Møller–Plesset perturbation theory and coupled cluster theory), seek to describe electronic correlation with increasing accuracy. Density functional theory (DFT) offers a different route by modeling exchange and correlation through functionals of the electron density, often with favorable computational scaling. Basis sets, which provide a mathematical description of atomic orbitals, and various extensions for excited states, spectroscopy, and solids, are integral to practical calculations. For excited states, time-dependent DFT and advanced wavefunction methods enable predictions of absorption spectra and photochemical behavior. In solid-state contexts, periodic boundary conditions and plane-wave or localized basis techniques extend quantum chemistry to materials science.

Applications span molecular structure and energetics, reaction pathways and transition states, vibrational and electronic spectroscopy, catalysis, materials design, and drug discovery. The approach is complementary to experimental methods, providing insights that can interpret measurements and guide experiments. Limitations include the computational cost of high-accuracy methods and the dependence of results on chosen functionals or basis sets, necessitating careful validation against benchmark data. Software packages and ongoing methodological developments continually expand the scope and reliability of kvantkeemiat.