abinitioAnsätzen

Ab initio methods, also known as first-principles calculations, are a class of computational quantum mechanical methods used in physics, chemistry, and materials science to predict the properties of molecules and condensed phases without the use of experimental data or empirical parameters. The term "ab initio" is Latin for "from the beginning." These methods rely on the fundamental laws of quantum mechanics, primarily the Schrödinger equation, to solve for the electronic structure of a system.

The core idea behind ab initio methods is to approximate the solution to the many-body Schrödinger equation. This is typically done by simplifying the problem, often by assuming that each electron moves independently in an average field created by all other electrons and the atomic nuclei. The most common ab initio method is Density Functional Theory (DFT), which reformulates the problem in terms of the electron density rather than the complex many-electron wavefunction. Other ab initio methods include Hartree-Fock theory and more advanced correlated wavefunction methods like Coupled Cluster.

The accuracy of ab initio calculations is highly dependent on the approximations made in solving the Schrödinger equation and the quality of the basis sets used to represent the atomic orbitals. Despite these approximations, ab initio methods can provide remarkably accurate predictions for a wide range of properties, including molecular geometries, vibrational frequencies, reaction energies, electronic band structures, and magnetic properties. They are widely used to study systems that are difficult or impossible to investigate experimentally, to interpret experimental results, and to design new materials.