  A method based on separated integration to estimate anharmonic corrections to
energy and vibration of molecules in a second-order diagrammatic vibrational
many-body Green's function formalism has already been presented. A severe
bottleneck in extending this approach to bigger molecules is that the storage
of the Green's function scales exponentially with the number of atoms in the
molecule. In this article, we present a method that overcomes this limitation
by approximating the Green's function in the Hierarchical Tucker tensor format.
We illustrate that the storage cost is linear in dimension and hence one can
obtain accurate representations of the Green's function for a molecule of any
size. Application of this method to estimate the second-order correction to
energy of molecules illustrates the advantage of this approach.
