The quantum-mechanical lattice theory in thermal-accommodation-coefficient theory is approached from the same point of view as the lattice theory of neutron scattering and Mössbauer effects. Treating the surface atoms from a displacement-field-theoretic point of view, rather than from the customary single-particle point of view, is more consistent with other solid-state theories. Virtual-phonon processes occurring in the field formulation give rise to a nontrivial modification in existing single-phonon accommodation-coefficient theories. This modification takes the form of a pseudo-Debye-Waller factor. When the existing theoretical accommodation coefficients are modified by the pseudo-Debye-Waller factor, it is found that the resulting accommodation coefficient, obtained herein, displays trends similar to experimental data for helium accommodation on tungsten.