Hartrees

Hartrees, or the Hartree energy, is a unit of energy used in atomic units. It provides a natural energy scale for atomic and molecular systems and is widely used in computational quantum chemistry, condensed matter physics, and related fields.

One Hartree energy Eh is defined as e^2/(4π ε0 a0), with e the elementary charge, ε0 the vacuum permittivity, and a0 the Bohr radius. It is equal to 2 times the Rydberg energy, about 27.2114 eV, or 4.3597×10^-18 joules.

In atomic units, several fundamental constants are set to unity: electron mass, elementary charge, the reduced Planck constant, and Coulomb's constant 1/(4π ε0). Consequently, energies are expressed in Hartrees, lengths in Bohr radii, and times in ħ/Eh.

Practically, Hartrees are common in electronic structure calculations, such as Hartree-Fock and density functional theory. When necessary, energies can be converted to electronvolts or kilojoules per mole; 1 Hartree equals about 27.2114 eV or 2625.5 kJ/mol.

The unit is named after Douglas Hartree, a British physicist and pioneer of numerical methods for solving the Schrödinger equation.