  Structures of excited states in $^{11}$B are investigated with a method of
$\beta$-$\gamma$ constraint antisymmetrized molecular dynamics in combination
with the generator coordinate method. Various excited states with developed
cluster core structures are suggested in positive- and negative-parity states.
For negative-parity states, we suggest a band with a $2\alpha+t$ cluster
structure. This band starts from the $3/2^{-}_{3}$ state and can correspond to
the experimental band observed recently. In positive-parity states, two
$\alpha$ core cluster structures with surrounding nucleons are found. A
$K^\pi=1/2^+$ band is suggested to be constructed from a remarkably developed
cluster structure with a large prolate deformation. We discuss features of the
cluster structure in association with molecular orbital structures of
$^{10}$Be.

Nuclear Theory