Determination of fundamental properties of nitrogen from first principles. I. Atomic polarizabilities and long-range dispersion coefficients

This work is the first in a series of papers in which we perform theoretical calculations of various fundamental properties of nitrogen relevant for gas thermometry experiments. In this part, we focus on the properties of the nitrogen atom, namely, dynamic polarizabilities and dispersion coefficients that describe interaction between two nitrogen atoms at large internuclear separations. These quantities are calculated using a composite scheme based on coupled cluster and full configuration interaction methods and large Gaussian basis sets optimized specifically for the purposes of this work. The dispersion coefficients, Cn with n = 6, 8, 10, are obtained using Casimir-Polder formulas by numerical integration over dipole, quadrupole, and octupole polarizabilities for imaginary frequencies represented analytically by Padé approximants. Special attention is paid to careful error control and uncertainty estimation of the calculated quantities.