  Densities of states for simple (sc) and base-centered (bcc) cubic lattices
with account of nearest and next-nearest neighbour hopping integrals $t$ and
$t'$ are investigated in detail. It is shown that at values of $\tau \equiv
t'/t = \tau_\ast$, corresponding to the change of isoenergetic surface
topology, the formation of van Hove $\bf k$ lines takes place. At small
deviation from these special values, the weakly dispersive spectrum in the
vicinity of van Hove lines is replaced by a weak $\bf k$-dependence in the
vicinity of few van Hove points which possess huge masses proportional to
$|\tau - \tau_\ast|^{-1}$. The singular contributions to the density of states
originating from van Hove points and lines are considered, as well as the
change in the topology of isoenergetic surfaces in the $\bf k$-space with the
variation of $\tau$. Closed analytical expressions for density of states as a
function of energy and $\tau$ in terms of elliptic integrals, and power-law
asymptotics at $\tau = \tau_\ast$ are obtained. Besides the case of sc lattice
with small $\tau$ (maximum of density of states corresponds to energy level of
X $\bf k$-point), maximal value of the density of states is always achieved at
energies corresponding to \textit{inner} $\bf k$-points of the Brillouin zone
positioned in high-symmetry directions, and not at zone faces.
