Quantumchemical

Quantumchemical is an adjective used to describe methods, theories, and data associated with quantum chemistry—the application of quantum mechanics to problems in chemistry. In practice, quantumchemical approaches aim to predict molecular structures, energies, properties, and reaction pathways from first principles or with calibrated approximations.

The field is organized into several methodological families. Ab initio methods, such as Hartree-Fock and post-Hartree-Fock theories (MP2, CCSD(T)), solve the electronic Schrödinger equation with increasing accuracy but growing computational cost. Density functional theory offers a density-based alternative that is widely used for routine calculations. Semi-empirical quantum chemistry uses parameterized integrals to reduce cost, enabling rapid screening of large systems. Excited-state methods, including time-dependent density functional theory (TD-DFT) and equation-of-motion coupled-cluster theory (EOM-CC), extend quantumchemical techniques to spectra and photochemical processes. Basis sets and effective core potentials are employed to describe electron distributions and core relativistic effects.

Applications span predicting molecular geometries, vibrational frequencies, reaction energetics, and spectroscopic signatures, as well as studying materials, catalysis, and drug design. Quantumchemical data are often used to interpret experiments, guide synthesis, and populate computational databases.

Limitations include functional dependence in density functional theory, varying accuracy across systems, and substantial cost for high-accuracy methods or large molecules. Ongoing developments focus on relativistic and dispersion corrections, multi-reference techniques, and integration with machine learning and multiscale modeling.