  We examine the role of electrostatic interactions in the assembly of empty
spherical viral capsids. The charges on the protein subunits that make the
viral capsid mutually interact and are expected to yield electrostatic
repulsion acting against the assembly of capsids. Thus, attractive
protein-protein interactions of non-electrostatic origin must act to enable the
capsid formation. We investigate whether the interplay of repulsive
electrostatic and attractive interactions between the protein subunits can
result in the formation of spherical viral capsids of a preferred radius. For
this to be the case, we find that the attractive interactions must depend on
the angle between the neighboring protein subunits (i.e. on the mean curvature
of the viral capsid) so that a particular angle(s) is (are) preferred
energywise. Our results for the electrostatic contributions to energetics of
viral capsids nicely correlate with recent experimental determinations of the
energetics of protein-protein contacts in Hepatitis B virus [P. Ceres and A.
Zlotnick, Biochemistry {\bf 41}, 11525 (2002).
