Quantum locality and equilibrium properties in low-temperature parahydrogen: a multiscale simulation study.

Abstract

Parahydrogen, the spin-zero singlet form of molecular hydrogen, exists as a fluid between approximately 14 and 25 K. Classical simulation approaches produce unphysical solidification at these temperatures, making quantum mechanical treatment necessary. This study applied the classical-quantum adaptive resolution scheme (AdResS) to examine how far quantum delocalization effects extend spatially within the bulk fluid. A spherical quantum region of variable size was embedded in a classically described surrounding medium with quantum-derived effective potentials, connected via open thermodynamic boundaries. Pair distribution functions were computed for several quantum region sizes. The findings indicate that, across the 14–25 K temperature range, the quantum structural characteristics of parahydrogen are spatially local, meaning that an explicit quantum description of the entire bulk is not required to capture accurate equilibrium properties.

Mechanism

Using the AdResS adaptive resolution method, a quantum-treated spherical region was coupled to a classically described bulk via open boundaries; pair distribution functions computed at varying quantum region sizes demonstrated that quantum delocalization effects in parahydrogen are spatially local at 14–25 K.