  We present a general virial theorem for quantum particles with arbitrary
zero-range or finite-range interactions in an arbitrary external potential. We
deduce virial theorems for several situations relevant to trapped cold atoms:
zero-range interactions with and without Efimov effect, hard spheres, narrow
Feshbach resonances, and finite-range interactions. If the scattering length
$a$ is varied adiabatically in the BEC-BCS crossover, we find that the trapping
potential energy as a function of $1/a$ has an inflexion point at unitarity.

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