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N Makri

Publications and source records attributed to N Makri.

7 recordsLinked to original sources
PubMed2004

Quantum dynamics in simple fluids.

We use quantum-correction factors to calculate approximately the quantum velocity time-correlation function (TCF) of supercritical Lennard-Jones argon from the classical TCF. We find that for this quite classical system, several different quantum-correction schemes yield essentially identical results for the real and imaginary parts of the quantum TCF, and also agree well with the recent forward-backward semiclassical dynamics (FBSD) results of Wright and Makri [J. Chem. Phys. 119, 1634 (2003)]. We also consider a more quantum-mechanical fluid of lighter atoms (neon) at a lower temperature. In this case different quantum-correction schemes give different results. FBSD calculations show that the harmonic quantum correction factor works the best for this system

Journal Article↗
PubMed1999

Rigorous forward-backward semiclassical formulation of many-body dynamics.

A rigorous, yet practical semiclassical formulation of time correlation functions or expectation values is presented. The main idea is to combine the forward and backward propagation steps into a single semiclassical propagator for those degrees of freedom that are not probed in a calculation, while retaining an explicit two-propagator description of the observable low-dimensional system. The combined forward-backward treatment of the environment naturally leads to extensive cancellation and results in an action that is small on the scale of Planck's constant. As a consequence, the integrand is smooth and thus amenable to Monte Carlo sampling. At the same time, important nonclassical effects terms, arising from interference among multiple bounce solutions of the system component, are fully accounted for.

Journal Article↗
PubMed1999

Time-dependent quantum methods for large systems.

This review focuses on time-dependent methods suitable for simulating the quantum dynamics of processes in large clusters and condensed-phase environments. A number of mean field, quantum-classical, and quantum statistical approximations that avoid the conventional exponential scaling with the number of degrees of freedom are reviewed. In addition, rigorous semiclassical and path integral approaches are described that are feasible in certain physical situations. Select chemical applications illustrating the capabilities of these methods are discussed.

Journal Article↗
PubMed1996

Long-time quantum simulation of the primary charge separation in bacterial photosynthesis.

Accurate quantum mechanical simulations of the primary charge transfer in photosynthetic reaction centers are reported. The process is modeled by three coupled electronic states corresponding to the photoexcited chlorophyll special pair (donor), the reduced bacteriopheophytin (acceptor), and the reduced accessory chlorophyll (bridge) that interact with a dissipative medium of protein and solvent degrees of freedom. The time evolution of the excited special pair is followed over 17 ps by using a fully quantum mechanical path integral scheme. We find that a free energy of the reduced accessory chlorophyll state approximately equal to 400 cm(-1) lower than that of the excited special pair state yields state populations in agreement with experimental results on wild-type and modified reaction centers. For this energetic configuration electron transfer is a two-step process.

Bacteriochlorophylls↗