#  Francesco Paesani 

 



####  calendar\_today Date and Time 

 **April 13, 2016** 

 04:00PM - 06:00PM EDT 

####  pin\_drop Location 

 **MIT, Room 4-163**  



 

 



 

Professor Francesco Paesani, University of California, San Diego. "Feel the Interactions: Achieving Chemical Accuracy through Many-body Representations." Boston Theoretical Chemistry Talk.Abstract: Two of the most challenging problems at the intersection of electronic structure theory and computer simulations are the accurate representation of intermolecular interactions and the development of reduced-scaling algorithms applicable to large systems. To some extent, these two problems are antithetical, since the accurate calculation of intermolecular interactions requires correlated methods whose computational scaling with respect to system size precludes the application to large systems. In this talk, I will describe our many-body molecular dynamics (MB-MD) methodology that has been shown to enable computer simulations with chemical and spectroscopic accuracy from the gas to the condensed phase. MB-MD combines many-body (MB) potentials derived entirely from “first principles” with quantum molecular dynamics (MD) methods based on the path-integral formalism. Our MB potentials are built upon the many-body expansion of the interaction energy and contain explicit 2-body and 3-body terms represented by permutationally invariant polynomials obtained from the application of machine learning techniques to correlated electronic structure data. These terms smoothly transition into a sum of classical expressions for the electrostatic and dispersion energies that reproduce the correct asymptotic behavior. Similarly, many-body representations of the dipole moment and polarizability surfaces are derived. The combination of these many- body representations with quantum dynamics methods enables the simulation of (linear and nonlinear) infrared, Raman, and sum-frequency generation spectra, which can be directly compared with experiment without requiring any empirical frequency shift or ad hoc scaling of the spectral intensity. I will illustrate the accuracy and predictive power of our MB-MD methodology through the analysis of the properties of aqueous systems from the gas to the condensed phase, with a particular emphasis on nuclear quantum effects and vibrational spectroscopy.



 

 



 

 

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