Theoretical and Computational Chemical Sciences

at UT-Austin

~molecular focus.James R. ChelikowskyRon Elber· biomolecular dynamics; bioinformaticsGraeme Henkelman· condensed matter dynamics.Dmitrii E. Makarov· biopolymers, single molecule phenomena.Peter J. Rossky· dynamics in solution + amorphous materials.John F. Stanton· excited state structure, reactivity.Robert E. Wyatt· quantum dynamics of molecular systems.

~materials focusRoger T. Bonnecaze· interfacial phenomena, fluid dynamics.James R. Chelikowsky· computational materials science.Venkat Ganesan· advanced polymeric materials.Gyeong S. Hwang· dynamics of solid state materials.Peter J. RosskyIsaac C. Sanchez· statistical thermodynamics of polymers.Thomas M. Truskett· energy landscapes -complex systems.

Faculty in Theoretical Chemistry

Chemistry Chemical Engineering

Rossky group researchRossky group researchDepartment of Chemical Engineering

Center for Computational Molecular Science (ICES)and Department of Chemistry and Biochemistry

MolecularMolecular mechanisms for chemical behavior - liquids / solutions / amorphous materials

Methods - Theory and simulationclassical and quantum statistical mechanics

at an atomistic and electronic level

Recent/current projects

solvent influences - biopolymer hydration protein interactions/stability- supercritical fluids: surfactants for novel solvents

condensed phase electronic and nuclear quantum dynamics- development of feasible algorithms for large systems- photochemistry; molecular electronic materials- spectroscopy, esp. ultrafast transient spectroscopy

Classical, atomistic, molecular dynamics simulation

‘Solvation’-

Hydration of biopolymer interfaces -role of chemical character and topology

Stability at low temperature –onset of cold unfolding; relation to cryopreservation?

Supercritical solvents (w/ Keith Johnston, ChE)

CO2 – solubility and interfaces -conceptual basis for surfactant design:

H2O microemulsionsnanoparticle synthesis and dispersion

rational ligand design

Simulation details:A neutron diffraction structure for sperm whale myoglobin was used as the starting point for simulations (PDB ID: 1CQ2). The HEME was removed, and the structure was fully solvated (SPC/E water). Simulation was run using NAMD program in the NPT ensemble at 510K and 1atm for 2ns.

2. Eliezer, D., Wright, P. E.“Is Apomyoglobin a Molten Globule? Structural Characterization by NMR”.

263, 531-538J. Mol.

Biol. 1996,

Apomyoglobin -Cold denaturation

Snapshots of SC changeSnapshot of VAL 114 at 310K (left) and 278K (right) near the end of the simulations runs. At 310K the residue is buried inside a hydrophobic pocket, but at 278K it is exposed to and surrounded by solvent.

Snapshot of ARG 45 at 310K (left) and 278K (right) near the end of the simulation runs. At 310K the pocket next to the residue is quite narrow and water cannot penetrate within. At 278K however, the interstitial space increases and water is in contact with the non-polar atoms within the pocket.

310K 278K

harmonic

ΔΔRMS atomic fluctuations onRMS atomic fluctuations on coolingcooling

Local isothermal compressibilityLocal isothermal compressibilityvolume fluctuations for atom groups based on space tesselation,

(following C. B. Post)

310K

278K

largest “anomalies”lie in the core.

enhanced position fluctuations

enhanced compressibility

UPON COOLING

Fig. 5“FRONT” “SIDE”

“hot spots” are in the CORE, not surface

CorrelationsCorrelations

enhanced atomic position fluctuations

regions of enhanced compressibility(“free volume”)

g (r)

Electronic / nuclear dynamics, and spectroscopy(methods + applications of quantum-classical/semiclassical simulation)

photochemistryexcited state dynamics and relaxationelectron transfer

electronic excitations and structure

organic electronic materials –energy trapping and transportphotoexcited statescharge carrier dynamics

clusters as models of bulk solvents –solvated electrons in water clusters

hν

π-electrons + molecular mechanics

Abs

PL

DIMERS – 2 x 5-mer @ 300K (in vacuo) 90 carbon atom system

Ground state optical absorption spectrum -“H-aggregate”-like: S2 is bright state

Excited state energy gaps (S2-S1): strongly modulated by structural fluctuations -

benzoid-quinoid shift ←→ Δ[charge]

Exciton (S1) localization and hopping in 2 x (5)OPV- contour plot of DR2

Delayed polaron pair formation in 2 x (7)OPV~ 3.1 eV initial excitation into S2 delayed formation ~ 20% cases ultrafast formation (< ~50 fs) ~ 15% cases

This example: delayed NA transition

to S1 via S3 at t ~ 500 fs

NA transition of an S2 EX to S1 PP never seen.

Delayed polaron pair formation in 2 x (7)OPV~ 3.1 eV initial excitation into S2 delayed formation ~ 20% cases ultrafast formation (< ~50 fs) ~ 15% cases

This example: delayed NA transition

to S1 via S3 at t ~ 500 fs

NA transition of an S2 EX to S1 PP never seen.

THANKS FOR YOUR ATTENTION!

THANKS FOR YOUR ATTENTION!