"description":"The long-range van der Waals energy between two non overlapping fragments A and B of the physical system under study can be expressed as a multipolar expansion and C_{n}^{AB} are the multipolar vdW coefficients. A widespread approach to include long-range vdW interactions in atomistic calculation is to truncate multipolar expansion to the dipole-dipole order and keep only the leading C_{6}^{AB} /R^{6} term. The vdW C_{6} coefficient can be obtained using Casimir-Polder integral over frequency dependent polarizability as function of imaginary frequency argument.",

"description":"The van der Waals radius, of an atom or molecule is the radius of an imaginary sphere representing the distance of closest approach for another atom(s). The vdW radius corresponds to half of the distance between two atoms where the Pauli repulsion balances the London dispersion attraction",

"description":"Atomic spin multiplicity. The multiplicity of an energy level is defined as 2S+1, where S is the total spin angular momentum. States with multiplicity 1, 2, 3, 4, 5 are respectively called singlets, doublets, triplets, quartets and quintets.",

"description":"In electronic structure theory, calculations may be performed for a spectrum with many excited energy levels. Molecular orbitals (MOs) are made of fractions of atomic orbitals. All atoms in the molecule provide their atomic orbitals for construction of MOs, but not all atomic orbitals must participate in all MOs. For example, the Hartree--Fock method for atoms or molecules assumes that the wave function is a single configuration state function with well-defined quantum numbers and that the energy level is not necessarily the ground state. The highest occupied molecular orbital state for a system is called as HOMO.",

"description":"In electronic structure theory, calculations may be performed for a spectrum with many excited energy levels. Molecular orbitals (MOs) are made of fractions of atomic orbitals. All atoms in the molecule provide their atomic orbitals for construction of MOs, but not all atomic orbitals must participate in all MOs. For example, the Hartree--Fock method for atoms or molecules assumes that the wave function is a single configuration state function with well-defined quantum numbers and that the energy level is not necessarily the ground state. The lowest unoccupied molecular orbital state for a system is called as LUMO.",

"description":"Ionization potential for free atom. The ionization potential is qualitatively defined as the amount of energy required to remove the most loosely bound electron or the valence electron, of an isolated gaseous atom to form a cation.",

"description":"Electron affinity for free atom. The electron affinity of an atom is the amount of energy released or spent when an electron is added to a neutral atom in the gaseous state to form a negative ion.",

"description":"The term symbol ({2S+1}^L_{J}) is an abbreviated description of the (total) angular momentum quantum numbers in a multi-electron atom (even a single electron can also be described by a term symbol). Each energy level of an atom with a given electron configuration is described by not only the electron configuration but also its own term symbol, as the energy level also depends on the total angular momentum including spin. The usual atomic term symbols assume LS coupling (also known as Russell-Saunders coupling or Spin-Orbit coupling). The ground state term symbol is predicted by Hund's rules.",

"description":"The term symbol ($^{2S+1}L_{J}$) is an abbreviated description of the (total) angular momentum quantum numbers in a multi-electron atom (even a single electron can also be described by a term symbol). Each energy level of an atom with a given electron configuration is described by not only the electron configuration but also its own term symbol, as the energy level also depends on the total angular momentum including spin. The usual atomic term symbols assume LS coupling (also known as Russell-Saunders coupling or Spin-Orbit coupling). The ground state term symbol is predicted by Hund's rules.",