Mode 'calpha' in Normal Modes gene does not work

[jaimergp]

Using this mode in the tests result in error at prody/dynamics/sampling.py:

def sampleModes(modes, atoms=None, n_confs=1000, rmsd=1.0):

        if not isinstance(modes, (Mode, NMA, ModeSet)):
            raise TypeError('modes must be a NMA or ModeSet instance, '
                            'not {0}'.format(type(modes)))
        if not modes.is3d():
            raise ValueError('modes must be from a 3-dimensional model')
        n_confs = int(n_confs)
        n_atoms = modes.numAtoms()
        initial = None
        if atoms is not None:
            if not isinstance(atoms, (Atomic)):
                raise TypeError('{0} is not correct type for atoms'
                                .format(type(atoms)))
            if atoms.numAtoms() != n_atoms:
>               raise ValueError('number of atoms do not match')

The relevant code on our end was written long ago by somebody who is not working here anymore, so we can expect some rough edges.