  We show that for n-dimensional Einstein gravity coupled to a scalar field
with mass-squared m_0^2=-n(n-2)/(4\ell^2), the first law of thermodynamics of
(charged) AdS black holes will be modified by the boundary conditions of the
scalar field at asymptotic infinity. Such scalars can arise in gauged
supergravities in four and six dimensions, but not in five or seven. The result
provides a guiding principle for constructing designer black holes and solitons
in general dimensions, where the properties of the dual field theories depend
on the boundary conditions.
