A Many-Body Perspective of Nuclear Quantum Effects in Aqueous Clusters

Nuclear quantum effects play an important
role in the structure
and thermodynamics of aqueous systems. By performing a many-body expansion
with nuclear-electronic orbital (NEO) theory, we show that proton
quantization can give rise to significant energetic contributions
for many-body interactions spanning several molecules in single-point
energy calculations of water clusters. Although zero-point motion
produces a large increase in energy at the one-body level, nuclear
quantum effects serve to stabilize higher-order molecular interactions.
These results are significant because they demonstrate that nuclear
quantum effects play a nontrivial role in many-body interactions of
aqueous systems. Our approach also provides a pathway for incorporating
nuclear quantum effects into water potential energy surfaces. The
NEO approach is advantageous for many-body expansion analyses because
it includes nuclear quantum effects directly in the energies.