Showing papers by "Andreas W. Götz published in 2018"

Comparison of permutationally invariant polynomials, neural networks, and Gaussian approximation potentials in representing water interactions through many-body expansions

Abstract: The accurate representation of multidimensional potential energy surfaces is a necessary requirement for realistic computer simulations of molecular systems. The continued increase in computer power accompanied by advances in correlated electronic structure methods nowadays enables routine calculations of accurate interaction energies for small systems, which can then be used as references for the development of analytical potential energy functions (PEFs) rigorously derived from many-body (MB) expansions. Building on the accuracy of the MB-pol many-body PEF, we investigate here the performance of permutationally invariant polynomials (PIPs), neural networks, and Gaussian approximation potentials (GAPs) in representing water two-body and three-body interaction energies, denoting the resulting potentials PIP-MB-pol, Behler-Parrinello neural network-MB-pol, and GAP-MB-pol, respectively. Our analysis shows that all three analytical representations exhibit similar levels of accuracy in reproducing both two-body and three-body reference data as well as interaction energies of small water clusters obtained from calculations carried out at the coupled cluster level of theory, the current gold standard for chemical accuracy. These results demonstrate the synergy between interatomic potentials formulated in terms of a many-body expansion, such as MB-pol, that are physically sound and transferable, and machine-learning techniques that provide a flexible framework to approximate the short-range interaction energy terms.

Force Field for Water over Pt(111): Development, Assessment, and Comparison.

Abstract: Metal/water interfaces are key in many natural and industrial processes, such as corrosion, atmospheric, or environmental chemistry. Even today, the only practical approach to simulate large interfaces between a metal and water is to perform force-field simulations. In this work, we propose a novel force field, GAL17, to describe the interaction of water and a Pt(111) surface. GAL17 builds on three terms: (i) a standard Lennard-Jones potential for the bonding interaction between the surface and water, (ii) a Gaussian term to improve the surface corrugation, and (iii) two terms describing the angular dependence of the interaction energy. The 12 parameters of this force field are fitted against a set of 210 adsorption geometries of water on Pt(111). The performance of GAL17 is compared to several other approaches that have not been validated against extensive first-principles computations yet. Their respective accuracy is evaluated on an extended set of 802 adsorption geometries of H2O on Pt(111), 52 geometries derived from icelike layers, and an MD simulation of an interface between a c(4 × 6) Pt(111) surface and a water layer of 14 A thickness. The newly developed GAL17 force field provides a significant improvement over previously existing force fields for Pt(111)/H2O interactions. Its well-balanced performance suggests that it is an ideal candidate to generate relevant geometries for the metal/water interface, paving the way to a representative sampling of the equilibrium distribution at the interface and to predict solvation free energies at the solid/liquid interface.

Comparison of permutationally invariant polynomials, neural networks, and Gaussian approximation potentials in representing water interactions through many-body expansions.

Abstract: The accurate representation of multidimensional potential energy surfaces is a necessary requirement for realistic computer simulations of molecular systems The continued increase in computer power accompanied by advances in correlated electronic structure methods nowadays enable routine calculations of accurate interaction energies for small systems, which can then be used as references for the development of analytical potential energy functions (PEFs) rigorously derived from many-body expansions Building on the accuracy of the MB-pol many-body PEF, we investigate here the performance of permutationally invariant polynomials, neural networks, and Gaussian approximation potentials in representing water two-body and three-body interaction energies, denoting the resulting potentials PIP-MB-pol, BPNN-MB-pol, and GAP-MB-pol, respectively Our analysis shows that all three analytical representations exhibit similar levels of accuracy in reproducing both two-body and three-body reference data as well as interaction energies of small water clusters obtained from calculations carried out at the coupled cluster level of theory, the current gold standard for chemical accuracy These results demonstrate the synergy between interatomic potentials formulated in terms of a many-body expansion, such as MB-pol, that are physically sound and transferable, and machine-learning techniques that provide a flexible framework to approximate the short-range interaction energy terms

N2O5 at water surfaces: binding forces, charge separation, energy accommodation and atmospheric implications

Abstract: Interactions of N2O5 with water media are of great importance in atmospheric chemistry and have been the topic of extensive research for over two decades. Nevertheless, many physical and chemical properties of N2O5 at the surface or in bulk water are unknown or not microscopically understood. This study presents extensive new results on the physical properties of N2O5 in water and at the surface of water, with a focus on their microscopic basis. The main results are obtained using ab initio molecular dynamics and calculations of a potential of mean force. These include: (1) collisions of N2O5 with water at 300 K lead to trapping at the surface for at least 20 ps and with 95% probability. (2) During that time, there is no N2O5 hydrolysis, evaporation, or entry into the bulk. (3) Charge separation between the NO2 and NO3 groups of N2O5, fluctuates significantly with time. (4) Energy accommodation of the colliding N2O5 at the surface takes place within picoseconds. (5) The binding energy of N2O5 to a nanosize amorphous ice particle at 0 K is on the order of 15 kcal mol−1 for the main surface site. N2O5 binding to the cluster is due to one weak hydrogen bond and to interactions between partial charges on the N2O5 and on water. (6) The free-energy profile was calculated for transporting N2O5 from the gas phase through the interface and into bulk water. The corresponding concentration profile exhibits a propensity for N2O5 at the aqueous surface. The free energy barrier for entry from the surface into the bulk was determined to be 1.8 kcal mol−1. These findings are used to interpret recent experiments. We conclude with implications of this study for atmospheric chemistry.

A Water Dimer Shift Activates a Proton Pumping Pathway in the PR → F Transition of ba3 Cytochrome c Oxidase.

Abstract: Broken-symmetry density functional calculations have been performed on the [Fea34+,CuB2+] state of the dinuclear center (DNC) for the PR → F part of the catalytic cycle of ba3 cytochrome c oxidase (CcO) from Thermus thermophilus (Tt), using the OLYP-D3-BJ functional. The calculations show that the movement of the H2O molecules in the DNC affects the pKa values of the residue side chains of Tyr237 and His376+, which are crucial for proton transfer/pumping in ba3 CcO from Tt. The calculated lowest energy structure of the DNC in the [Fea34+,CuB2+] state (state F) is of the form Fea34+═O2–···CuB2+, in which the H2O ligand that resulted from protonation of the OH– ligand in the PR state is dissociated from the CuB2+ site. The calculated Fea34+═O2– distance in F (1.68 A) is 0.03 A longer than that in PR (1.65 A), which can explain the different Fea34+═O2– stretching modes in P (804 cm–1) and F (785 cm–1) identified by resonance Raman experiments. In this F state, the CuB2+···O2– (ferryl–oxygen) distance is only...