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Quantum Chemistry Techniques, with Ali Alavi, University of Cambridge

Image:  Dr Mariana Rossi
Dr Mariana Rossi

Date: 12 April 2019   Time: 15:00 - 16:00

Quantum Chemistry Techniques, with speakers:

Mariana Rossi, Fritz-Haber Institut of the Max Planck Society,

Sotiris Xantheas, Pacific Northwest National Laboratory


Mariana Rossi
Addressing the structure and dynamics of weakly-bonded interfaces

Abstract: Interfaces between different materials constitute the basis of many technological devices. Incorporating organic components within different architectures opens the path for creating more versatile interfaces with a wide range of properties at a reduced cost. However, the large conformational space that organic components can explore at finite temperatures and the inherent anharmonicity of their intra and intermolecular interactions brings further challenges to first-principles simulations. In this talk, I will discuss our recent efforts to address these challenges, based on developments within density functional theory an ab initio (path integral) molecular dynamics. I will present strategies for conformational space sampling of organic/inorganic interfaces, discuss the relationship between atomic and electronic structure, present techniques to include anharmonicity in vibrational fingerprints and machine learning tools to calculate these at reduced costs, and our recent methodological developments that allow the inclusion of quantum nuclear effects in high-dimensional systems (especially weakly bonded interfaces) using path integral molecular dynamics.

Biography
Mariana was born in Campinas, SP, Brazil, and studied Physics (bachelors and masters) in the University of São Paulo. During her junior project and master studies she started working with electronic structure theory and theories for charge transport under the supervision of Prof. Antônio José Roque da Silva and Prof. Adalberto Fazzio. She then moved to Berlin, Germany, to do her PhD in the Fritz Haber Institute of the Max Planck Society, under the supervision of Prof. Volker Blum and Prof. Matthias Scheffler. In her PhD she worked with structure determination of biomolecules from first-principles electronic structure methods. She focused on structure search and use of ab initio molecular dynamics to compute thermodynamical and vibrational properties of these systems. Her first post-doc was at the University of Oxford with Prof. David Manolopoulos, where she learned about path integral methods and approximate quantum dynamics, focusing her work on the inclusion of nuclear quantum effects in dynamical observables. She visited the group of Prof. Michele Ceriotti in École Polytechnique Fédèrale de Lausanne for one year, where she continued joining ab initio and path integral simulations for the calculations of thermodynamic properties of hydrogen-bonded systems. Since October 2016, she is back at the Fritz Haber Institute of the Max Planck Society in Berlin as an Otto-Hahn group leader. The group focuses on the study of H-bonded systems composed of biomolecules, organic molecules, and their interfaces with inorganic systems. Mariana was awarded fellowship for her master studies from the São Paulo Research Foundation (FAPESP), a Deutsche Forschungsgemeinschaft fellowship for post-doctoral studies, a Junior Research Fellowship at St. Edmund Hall in Oxford, and the Otto Hahn Award of the Max Planck Society.



Sotiris Xantheas, Pacific Northwest National Laboratory
Advanced Computing, Mathematics and Data Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, MS K1-83, WA, 99352, USA
Department of Chemistry, University of Washington, Seattle, WA 98195, USA


The many-body expansion for aqueous systems revisited

We revisit the Many-Body Expansion (MBE) for water-water interactions by examining the effects of the basis set, including those resulting from the Basis Set Superposition Error (BSSE) correction, on the various terms for selected sizes of water clusters up to n = 21. The analysis is performed at the second order Møller-Plesset (MP2) perturbation theory with the family of augmented correlation consistent basis sets up to five zeta quality for the (H2O)n, n = 7, 10, 13, 16 and 21 clusters, for which we report either the complete MBE (n = 7, 10) or the one through the 6-body (n = 13) and the 5-body terms (n = 16, 21). Our results suggest that any sizeable contributions to the total cluster binding energy arising from the 5-body and larger terms are solely an artifact of the finite basis set. Indeed, all terms above the 4-body converge to practically zero at the Complete Basis Set (CBS) limit and this finding is accurately reproduced even with the smaller basis set of the series (aug-cc-pVDZ) once the BSSE correction is considered. The same level of theory (MP2/aug-cc-pVDZ, BSSE-corrected) also accurately reproduces the magnitude of the 3- and 4-body terms, for which we also find that the contributions of electron correlation are quite small. Our results unquestionably demonstrate that the MBE for water-water interactions vanishes monotonically with basis set size and can be safely truncated at the 4-body term once BSSE corrections are considered. We expect these findings to have important consequences in the pursuit of accurate many-body molecular dynamics simulations for aqueous systems.


* This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory (PNNL) is a multi-program national laboratory operated for DOE by Battelle.

Location:  G21 Ramsay Lecture Theatre, followed by a reception in the Nyholm Room, Department of Chemistry, UCL
Contact:  Karen Stoneham
Email:  tyc-administrator@ucl.ac.uk
Website:  http://www.thomasyoungcentre.org/events/quantum-chemistry-techniques/