Set to a non-zero value to add a long-range correction for solids to the kernel.
This is the $\alpha$ parameter defined in S. Botti et al., Phys. Rev. B
69, 155112 (2004). The $\Gamma = \Gamma = 0$ term $-\alpha/q^2$ is taken into account by introducing an additional pole to the polarizability (see R. Stubner <i>et al.</i>, <i>Phys. Rev. B</i> 70, 245119 (2004)). The rest of the terms are included by multiplying the Hartree term by $1 - \alpha / 4 \pi$. The use of non-zero $\alpha$ in combination with <tt>HamiltonianVariation</tt> = <tt>V_ext_only</tt> corresponds to account of only the $\Gamma = \Gamma = 0$ term.
Applicable only to isotropic systems. (Experimental)