Greater Boston Area Theoretical Chemistry Lecture Series

2013-2014 Speaker Schedule

How to do research by changing notation

10/02/13 4:00pm - CANCELLED

MIT Building 4, Room 163

Atilla Szabo

NIDDK, National Institute of Health




David Manolopoulos

The interrelation among the following will be discussed: particle-in-a box, Huckel theory, harmonic oscillator, the polarizability of the hydrogen atom, trapping and first passage times, free energy of a confined random coil, turnover times in enzyme catalysis, gambler's ruin, kinetics of ligand binding to hemoglobin, Levinthal's paradox in protein folding, cyclization of a polymer, and force induced rupture of a single molecule.

Ab initio colors

10/24/13 4:00pm

Harvard

Stefano Baroni

Scuola Internazionale Superiore di Studi Avanzati




Stefano Baroni

I will present some recent work addressing the effects of the solvent (water) on the optical properties of natural dyes. I will break the ice with a short presentation of the physics and physiology of color vision, in the style of popular science. I will then introduce some of the theoretical and computational techniques that are currently being used to model the optical properties of complex molecular systems and nano- structured materials, based on time-dependent density-functional perturbation theory. These techniques will be demonstrated with the "prediction" that grass is green, and applied to the optical properties of flavylium, the die that gives aubergines and blueberries their typical deep-purple coloration, as well as of other anthocyanins. I will show that the main effect of the solvent is to provide a medium allowing thermal fluctuations to fill the gaps that would otherwise characterize the spectrum of the dye at low temperature, thus considerably enhancing optical absorption in the visible range, and making blueberries (deep) blue. The uncertainties due to the inadequacies of current energy functionals will be discussed, along with the prospects of predicting and engineering the color optical properties of anthocyanins in solution.

Seeking a sustainable model for scientific simulation

11/06/13 4:00pm

MIT Building 4, Room 163

Robert Harrison

Brookhaven National Laboratory




Robert Harrison

Many are now questioning whether our current approaches to developing software for science and engineering are sustainable. In particular, can we deliver to society and the nation the full benefits expected from high-performance simulation at the peta and exascales? Or is innovative science being stifled by the increasing complexities of all aspects of our problem space (rapidly changing hardware, software, multidisciplinary physics, etc.)?

Focusing on applications in chemistry and materials science, and motivated co-design of exascale hardware and software, I will discuss many of these issues including how chemistry has already been forced to adopt solutions that differ quite sharply to those in the mainstream, and how these solutions position us well for the technology transitions now under way. Radical changes in how we compute, going all the way back to the underlying numerical representation and algorithms used for the simulation, also promise great enhancements to both developer productivity and the accuracy of simulations.

Electron correlation in density functional and coupled cluster theory

12/04/13 4:00pm

MIT Building 4, Room 163

Fred Manby

Bristol University




Fred Manby

Electron correlation is treated very differently in density functional theory and in wavefunction-based methods like coupled-cluster theory. Here I will show that there are some interesting points of connection, illustrated first through a new kind of correlation functional derived from many-body theory using the Unsöld approximation; and second through an intriguing modification of coupled-cluster theory that probes one of the most dogmatically accepted assumptions of electronic structure theory: that one should never contemplate breaking the Pauli principle.

Quantum-Classical Dynamics: Issues and Applications

12/11/13 4:00pm

MIT Building 4, Room 163

John Tully

Yale University




John Tully

Conventional Molecular Dynamics (MD) rests on two fundamental assumptions: 1. Nuclear motion evolves by classical mechanics. 2. The forces on the nuclei derive from a single electronic potential energy surface (the Born-Oppenheimer Approximation). There are hosts of chemical processes for which one or both of these assumptions are not adequate. Nuclear motion can exhibit pronounced quantum mechanical effects associated with tunneling, zero-point motion and quantized energy levels. Transitions among multiple electronic states can play a dominant role in processes such as nonradiative transitions, electron transfer, photochemistry, and chemistry at semiconductor and metal surfaces. Mixed quantum-classical dynamics (MQCD) has been an at least partially successful strategy for introducing quantum effects into molecular dynamics simulations, as well as providing a procedure to treat open systems. crucial concern in MQCD is feedback between the classical and quantum motions. The time-dependent motion of the classical nuclei induces transitions among quantum states. Quantum mechanical transitions, in turn, alter the forces that govern the motion of the classical particles. Proper treatment of this “quantum backreaction” has been a subject of controversy for more than 40 years. Aspects of this issue will be examined, both at a fundamental level and by example. Among the applications presented are the quantum dynamics of proton transfer in solution and inelastic scattering of molecules from metal surfaces. Because metal surfaces exhibit a continuum of infinitesimally spaced conduction electron levels, the latter is an extreme example of anticipated inadequacy of the Born-Oppenheimer Approximation.

Elementary processes in functional organic polymer materials: Does quantum coherence matter?

03/05/14 4:00pm

MIT Building 4, Room 163

Irene Burghardt

Goethe-Universitat




Irene Burghardt

As suggested by recent experimental studies, quantum coherence may be a driving force behind the ultrafast elementary processes in organic photovoltaics, very similarly to previous observations for biological light-harvesting systems. In this lecture, we will examine the intricate interplay of delocalized electronic excitations (i.e., electron-hole quasi-particle states, or excitons), electron-phonon coupling, and static and dynamic disorder, in order to assess the role of coherent transfer phenomena. The first part of the lecture will set the stage by introducing a vibronic coupling Hamiltonian in a generalized electron-hole representation, along with ab initio based parametrization strategies that include realistic phonon spectral densities. Quantum dynamical studies based upon this Hamiltonian are carried out using the Multi-Configuration Time-Dependent Hartree (MCTDH) method and non-Markovian reduced dynamics approaches. In the second part of the lecture, we will specifically address (i) the dynamics of exciton migration across a torsional defect that locally breaks the pi-conjugation in oligo-(p-phenylene vinylene) and oligothiophene fragments, and (ii) ultrafast exciton dissociation in typical donor-acceptor complexes representing models of polymer-fullerene heterojunctions. Rapid free carrier generation from the primary interfacial charge transfer (CT) state is shown to be feasible, due to an effective lowering of the Coulomb barrier as a result of charge delocalization, along with the vibronically hot nature of the primary CT state. Against this background, a perspective will be given on the connection between ultrafast charge separation and high internal quantum efficiencies.

Challenges and progress in atomistic molecular dynamics simulations

03/26/14 4:00pm

MIT Building 4, Room 163

Michele Parrinello

Eidgenossische Technische Hochschule Zurich




Michele Parrinello

The rapid development of computer technology and namely algorithms have had deep impact on science. Of particular significance has been the emergence of realistic atomistic simulation. These calculations provide precious insight, replace difficult experiments and predict new phenomenon. Yet in spite of remarkable progress much remain to be done to widen the scope of atomistic simulation, especially in the fields of nanotechnology and biosciences. This require extending the time and length scale of the system studied. Even more challenging is the need to find appropriate tools to describe and tame the complexity of the systems of current interest. We shall review progress in the field. And discuss in some details recent applications crystal growth from solution and to protein-ligand binding.

Plasmon-molecule interactions

04/02/14 4:00pm

MIT Building 4, Room 163

George Schatz

Northwestern University




George Schatz

This talk describes recent theory developments concerned with the optical properties of plasmonic materials, with emphasis on understanding plasmon enhanced spectroscopic techniques such as surface enhanced Raman spectroscopy (SERS), plasmon-enhanced photochemistry, and the coupling of plasmons to excitons. The cornerstone of this work is computational electromagnetics, which provides the ability to solve Maxwell's equations exactly for a given nanoparticle structure and with assumed dielectric functions. A number of methods for doing these calculations are available, and in the first part of the talk I will review how these calculations are done, and I will demonstrate their use to study the extinction spectra and SERS of silver and gold nanoparticles and other nanostructures. In addition, I will describe very recent applications concerned with the optical properties of nanoparticle superlattices that constitute a type of metamaterial that exhibits unusual optical properties.

The second half of the talk will focus on problems where one needs to couple classical electrodynamics for metal particles to quantum mechanics (usually TDDFT) for molecules near the nanoparticles. These theories will be developed both in the frequency and time domains, and the inclusion of both electromagnetic interactions and chemical interactions between the metal nanoparticle and molecular adsorbate are considered. We demonstrate the use of these methods with applications to SERS and to plasmonic solar cells. In addition, we describe examples of plasmon-exciton interactions, such as occurs in plasmon-enhanced lasing. Here we show how plasmons can interact with molecules to enhance both spontaneous and stimulated emission.

TBD

04/09/14 4:00pm

MIT Building 4, Room 163

Todd Martinez

Stanford University




Todd Martinez



TBD

TBD

May, 2014 4:00pm

MIT Building 4, Room 163

Ksenia Bravaya

Boston University




Ksenia Bravaya



TBD

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