Full gravitational potential inclusive loading contribution.
Given in the center of solid Earth (CE).
For Center of Mass (CM) set degree 1 coefficients to zero.
  cnm(t) = sum_f cnm.f.cos * cos(theta_f(t)) + cnm.f.sin * sin(theta_f(t))
  snm(t) = sum_f snm.f.cos * cos(theta_f(t)) + snm.f.sin * sin(theta_f(t))

Reference paper:
Hart-Davis M., Piccioni G., Dettmering D., Schwatke C., Passaro M., Seitz F.:
EOT20: a global ocean tide model from multi-mission satellite altimetry.
Earth System Science Data, 13, 3869–3884, doi: 10.5194/essd-13-3869-2021, 2021.

Converted into spherical harmonics by Torsten Mayer-Guerr.