The neutron powder diffraction and inelastic neutron scattering (INS) spectra of the electron donor-acceptor complex, tetracyanoethylene-hexamethylbenzene have been studied as a function of pressure to 0.414 GPa. Using the PW91 and PBE density functional theories, the unit cell vectors were calculated as a function of pressure and are compared to those experimentally obtained from the diffraction data. The calculated lattice vectors display large errors at low pressures but were found to be in close agreement with the experimental vectors at 0.414 GPa. Comparison of the experimental INS spectra of the TCNE-HMB enabled assignment of specific vibrational modes while providing a direct measurement of the effect of pressure on the complex. The PW91 vibrational frequency calculations reproduced both the vibrational intensities and frequencies with relative accuracy.