Dipole Polarizability of the Neutral Carbon Atom and the Dipole-Dipole Interaction between Carbon Atoms

Many-body perturbation theory is used to calculate the dipole polarizability ${\alpha }_d$ of the neutral carbon atom in its ${}_{}{}^3{}_{}{}^{}P$ ground state. The result is 2.38 ${\mathrm{\AA }}^3$ in lowest order. When correlations are included by calculating higher-order terms in the perturbation expansion, we obtain the value 1.54 ${\mathrm{\AA }}^3$ for ${\alpha }_d$ averaged over $M_L$ values. A calculation of the coefficient of the $R^{-6\mathrm{}}$ term in the van der Waals interaction between two carbon atoms each in the ${}_{}{}^3{}_{}{}^{}P$ ground state is also reported.