Quantemiska

Quantemiska, or quantum chemistry, is the branch of chemistry that uses quantum mechanics to explain and predict the properties and behavior of molecules. It focuses on electronic structure, potential energy surfaces, and spectroscopic properties, aiming to connect molecular structure with reactivity.

Computational approaches in quantemiska fall into two main families: wavefunction-based methods and density functional theory (DFT). Wavefunction methods include Hartree–Fock and post-Hartree–Fock techniques such as MP2, configuration interaction, and coupled-cluster methods (for example CCSD(T)). DFT uses approximations to electron density to estimate energies and properties, offering favorable accuracy-cost trade-offs. Time-dependent extensions (TD-DFT) provide access to excited states. Calculations rely on basis sets to describe molecular orbitals.

Applications include geometry optimization, vibrational frequencies, reaction energetics and mechanisms, and predictions of UV–visible spectra and NMR shifts. Quantum chemistry complements experimental work in catalysis, materials science, and drug design, guiding interpretation and design.

History: The field grew from early quantum theory and molecular orbital models in the 1920s–1930s, with the Born–Oppenheimer approximation and the Heitler–London treatment of H2. The Hartree–Fock method matured in the mid-20th century, followed by developments in post-HF methods. DFT became widely used in the 1990s and beyond, driven by computational efficiency.

Limitations include dependence on the chosen method and basis set, treatment of electron correlation, and computational cost that scales poorly with system size. For large systems, hybrid QM/MM approaches or semi-empirical methods are common. Nevertheless, quantemiska remains essential for understanding chemical phenomena and for guiding experiments and materials design.