Reactive path integral quantum simulations of molecules solvated in superfluid helium

This work theoretically examines the progressive coating of planar polycyclic aromatic hydrocarbon (PAH) molecules ranging from benzene to circumcoronene (C54H18) by para-hydrogen and ortho-deuterium. The coarse-grained Silvera-Goldman potential has been extended to model the interactions between hydrogen molecules and individual atoms of the PAH and parametrized against quantum chemical calculations for benzene-H2. Path-integral molecular dynamics simulations at 2 K were performed for increasingly large amounts of hydrogen coating the PAH up to the first solvation shell and beyond. From the simulations, various properties were determined such as the size of the first shell and its thickness as well as the solvation energy. The degree of delocalization was notably quantified from an energy landscape perspective, by monitoring the fluctuations among inherent structures sampled by the trajectories. Our results generally demonstrate a high degree of localization owing to relatively strong interactions between hydrogen and the PAH, and qualitatively minor isotopic effects. In the limit of large hydrogen amounts, the shell size and solvation energy both follow approximate linear relations with the numbers of carbon and hydrogen in the PAH.

Section: Discussionmentioning

confidence: 99%

Solvation of carbonaceous molecules by para-H2 and ortho-D2 clusters. I. Polycyclic aromatic hydrocarbons

Calvo

Yurtsever

2016

“…These issues would be better clarified using more advanced (but also more demanding) simulation techniques that account for exchange statistics. 58,59 V. CONCLUDING REMARKS The interaction between hydrogen and carbon nanostructures has received a lot attention owing to potential applications for reversible energy storage. 41,42,60,61 It also has implications in astrochemistry especially since the observation of fullerenes in the interstellar medium, 62,63 and the ubiquity of hydrogen in the Universe.…”

Section: Discussionmentioning

confidence: 99%

Solvation of carbonaceous molecules by para-H2 and ortho-D2 clusters. II. Fullerenes

Calvo

Yurtsever

2016

“…Thanks also to the native implementation of these techniques in the CP2k simulation package, this work will pave the way to the study of low temperature physics and cryochemistry, such as helium droplet spectroscopy of molecules, together with an ab initio treatment of interatomic forces that is enabled by the recently developed hybrid ab initio/bosonic PIMD/PIMC simulation technique 59,60 .…”

Section: Discussionmentioning

confidence: 99%

Accelerated path integral methods for atomistic simulations at ultra-low temperatures

Uhl

Marx

Ceriotti

2016

Self Cite

Path integral methods provide a rigorous and systematically convergent framework to include the quantum mechanical nature of atomic nuclei in the evaluation of the equilibrium properties of molecules, liquids or solids at finite temperature. Such nuclear quantum effects often are already significant for light nuclei at room temperature, but become crucial at cryogenic temperatures such as those provided by superfluid helium as a solvent. Unfortunately, the cost of converged path integral simulations increases significantly upon lowering the temperature so that the computational burden of simulating matter at the typical superfluid helium temperatures becomes prohibitive. Here we investigate how accelerated path integral techniques based on colored noise generalized Langevin equations, in particular the so called PIGLET variant, perform in this extreme quantum regime using as an example the quasi rigid methane molecule and its highly fluxional protonated cousin, CH + 5 . We show that the PIGLET technique gives a speedup of two orders of magnitude in the evaluation of structural observables and quantum kinetic energy at ultralow temperatures. Moreover, we computed the spatial spread of the quantum nuclei in CH 4 to illustrate the limits of using such colored noise thermostats close to the many body quantum ground state.