Optimal gauge in approximate calculations of molecular magnetic properties

✍ Scribed by P.A. Braun; T.K. Rebane

• Publisher: Elsevier Science
• Year: 1977
• Tongue: English
• Weight: 227 KB
• Volume: 49
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(77)80466-1

✦ Synopsis

A variational procedure is suggested for determining optimal gauge parameters (such as gauge origin etc.) in calculations of molecular magnetic properties with a finite basis set.

Magnetic properties of molecules (components

of magnetic susceptibility tensor, nuclear magnetic shielding and related properties) are gauge independent. However their approximate values calculated with a limited set of basis functions uk (k = 1.. . M) frequently show a strong dependence on the choice of the vector potential of the external uniform magnetic field or the field of the nuclear magnetic dipole moment. Optimal gauge choice in limited basis set calculations presents therefore an important problem which has been discussed in a number of articles (see e.g. refs. [I 21 and references therein). Nevertheless there is still no satisfactory solution.

In this paper a new approach to the problem of optimal gauge is suggested. It is based on a variational principle and may have a wide range of applications like other variational methods of quantum mechanics.

Let J/(u) be the unperturbed wavefunction of a 2nelectron system in a closed-shell state, assumed to be known exactly. It satisfies the equation