Daniel Neuhauser - US grants

9314320 Neuhauser Univ. Cal. Los Angeles This project in diatom-diatom reactive scattering theory is supported by the NSF Theoretical and Computational Chemistry Program. Exact, coupled-channel, state-to-state, quantum scattering, calculations will be carried out for gas phase reactions of diatomic molecules taking explicit account of all six degrees of internal freedom. Improved computational methods will be developed, in particular, a time-dependent and an equivalent time-independent flux-amplitude method, use of absorbing potentials, and an improved filter algorithm for the accurate computation of eigenvectors whose eigenvalues lie within a selected range. The first application of the theory will be to the reaction of molecular hydrogen with the hydroxyl radical. This research project develops improved computational methods for predicting the detailed behavior of a very simple chemical reaction. Rigorous quantum mechanical calculations will be carried out for a four-atom system. The goal is to obtain a detailed and precise picture of the atomic events that occur. This fundamental knowledge, which is difficult and expensive to extract from laser spectroscopy and other laboratory experiments, provides detailed information that serves to test various simplifying mathematical approximations used for practical calculations for gas phase reactions of larger molecules. The reaction of molecular hydrogen with the hydroxyl radical is itself of interest because it is an important step in the chain reaction that occurs during the combustion of hydrogen gas.

In this Faculty Early Career Development Award funded by the Theoretical and Computational Chemistry Program at NSF, Daniel Neuhauser at the Chemistry Department of the University of California at Los Angeles will investigate problems in three distinct research areas in molecular structure and molecular dynamics. The work in all three areas is based on related mathematical approaches for the efficient diagonalization of large matrices. The first area uses a Quantum Monte-Carlo approach to obtain accurate electronic wavefunctions and potential energy surfaces for molecular systems. The second area involves efficient solutions of path-integral simulations of molecular dynamics and scattering, both reactive and non-reactive. The third area involves the determination of the normal modes for the vibrations of proteins. Neuhauser's teaching plans include an increased emphasis on undergraduate research and the introduction of computational chemistry projects into undergraduate coursework. The work in each of these three areas of research will extend the understanding of the fundamental processes which underlie many important chemical reactions. The reactions to be studied initially in the first two areas were chosen because of their relevance to combustion processes. One of the goals of the studies of the normal modes in proteins, the third research area, is to obtain information necessary for the simulation of reactions involved in photosynthesis.

Dan Neuhauser is supported by a grant from the Theoretical and Computational Chemistry Program to continue his research on quantum molecular dynamics calculations of four-atom reactions. The method development will involve time-dependent simulations with spatial-grid reduction, and a Filter-Diagonalization-based hybrid approach. Crucial elementary combustion reactions will be chosen as the applications. A smaller portion of this research will concern extension of the Filter-Diagonalization method to semiclassical methodology, which is routinely employed for systems with many more degrees of freedom. Modern dynamical methods will be developed and applied to the study of four-atom chemical reactions. This class of reactions is fundamental to the fields of enviromental and combustion chemistry. Methodological extensions to reactions of more than four atoms will also be developed, since larger scale reactions are of interest in elucidating, for example, surface chemistry phenomena.

Divisions of Chemistry, and Bioengineering and Environmental Systems support this multidivisional award to University of California Los Angeles, and this award is part of the Nanoscale Exploratory Research in the Nanoscale Science and Engineering program. Under this project, Jeffrey Zink will synthesize nano-engineered photo-electrochemical cells by self assembly process using solution-based sol-gel process, which will replace time consuming step-by-step serial assembly process. This materials synthesis method will provide flexibility in the spatial configuration and the chemical environment of the photoelectron donors and acceptors. Theoretical studies will be performed to determine the charge separation and electron transport in the nanostructured materials. The research program will provide education and training opportunities in material chemistry to underrepresented groups in undergraduate education through the Student Research Participation and Center for Academic Excellence programs at University of California at Los Angeles.

Under the award, nano-engineered photo-electrochemical cells will be fabricated using a solution-based sol-gel self-assembly process. The process will yield ordered and oriented nanostructures of relatively large sizes for the development of photoelectrochemical devices. In addition, the research program will provide multidisciplinary education and training opportunities in materials chemistry to underrepresented groups in undergraduate education.

Dan Neuhauser of UCLA is supported by the Chemistry Division through the Information Technology Program to combine cross-correlation filter diagonalization and Monte Carlo methods to investigate low-lying excitation dynamics of helium clusters confined within aromatic structures or fullerene molecules. Three Monte Carlo approaches will be employed: trajectory dependent cellularization, imaginary-time diffusion Monte Carlo, and auxiliary-field Monte Carlo. The rise in computational power and the reduced cost of high-speed Linux computer clusters motivate this development of new approaches for quantum dynamics based on parallel computations.

The development of new methods to study spectra of large chemical systems on clusters of inexpensive, parallel computers demonstrates that formerly intractable quantum mechanical problems can benefit from the next generation of computing. Novel technical solutions such as those developed here will be useful in the more general context of signal processing and information extraction. Further, the investigations of fullerene-based encapsulation of molecules are of import to hydrogen storage applications.

Danny Neuhauser of UCLA is supported by the Theoretical and Computational Chemistry Program to explore and computationally test the concepts of quantum mechanical interference and resonance for possible use in single molecule conductance. He will search for new classes of molecules in which resonances and interference can be used to control conductivity, such as polycyclic hydrocarbons and crown ethers. He will also explore the response of the conductance to potential gradients, the presence of specific molecules, and the effects of two voltage gates. He will develop time-dependent density functional theory with absorbing boundaries to model local response, time-dependent polarization, dissipation, and the interplay between motion and conductance.

Single-molecule properties and conductivity in particular are potentially very important in characterizing and detecting nano-level properties and in using molecules as logic gates. The methodologies under development here will aid in understanding and applying chemistry on nano-scales, developing logic circuits, and devising improved sensors and approaches for coupling motion and conductivity on a single-molecule level.

The investigator and his colleagues propose a new paradigm-shifting approach towards high resolution and high contrast imaging, which combines revolutions in magnetic resonance imaging (MRI) and optical imaging with equally cutting edge mathematical developments.
The approach uses non-linear feedback between the detector and the sample, so that the measured field is fed back to the MRI magnet. The unstable feedback increases the dynamical contrast between normal and cancerous cells. This highly nontraditional approach will be complemented by incorporating compressed sensing, a data analysis technique where mathematical algorithms are used to extract specific features and images from a relatively small number of measurements.
Finally, multiple sources and detectors, which coupled with compressed sensing and feedback imaging can collect data in parallel will be implemented together, and modern filter-diagonalization techniques will be used to synthesize the data leading to faster images.

Overall, the research and development that the principal investigator and his colleagues propose will revolutionize MRI. By applying nontraditional measurement and imaging technique, the contrast between tumors and normal areas will be increased many fold. The increase will be based on the same physical phenomena, chaos, that is used to by birds and jet fighters to quickly switch their direction. The revolutionary paradigm will will eventually make it much cheaper and faster to do an MRI scan, thereby having enormously broad impacts. In 2008, an estimated 1,680,000 people in the U.S. will be diagnosed with cancer, and approximately 670,000 people will die. Between 10%-35% could have been saved with earlier detection.
This highlights the need for improved early detection methods, which could have saved many patients. A large (2-5 or more) reduction MRI acquisition time, which is not feasible with conventional methods, coupled with the enhanced feature resolution native to the proposed approach, will allow for faster and cheaper cancer screening, which is crucial to improved early detection and thus reducing deaths due to cancer. Besides cancer detection, there are numerous other imaging applications that stand to benefit from significantly decreased scan time and cost, such as industrial sensing (for example uniformity of fruits in agriculture) and homeland security applications, including highly sensitive detection of concealed materials.

Daniel Neuhauser of UCLA is supported by an award from the Theoretical and Computational Chemistry program for work to develop a theoretical methodology to understand molecular nanopolaritonics. The project is intended to unify the treatment of radiation and matter in such a way as to efficiently and accurately describe systems of arbitrary physical geometry and electronic structure. Prior to this reseach, combined plasmon-matter studies typically utilized multipole mode expansions on the plasmon-carrying structure, which although simple, are unable to accurately capture arbitrary geometries or field singularities. Using TDDFT for the whole system, on the other hand, is prohibitively expensive computationally. The PI is, thus, extending previous simulations, both in terms of method used and applications chosen for testing those methods. The research starts with FDTD-type algorithms (to be modified for near-field applications), and continues on to discrete-dipole studies, and finally implements embedding formalisms using Hydrodynamic Tensor DFT. The molecular part is being described by a real-time TDDFT algorithm, and treated non-linearly as to capture the multiharmonic and frequency mixing characteristics of the system.

The drive towards ever smaller scales for radiation features has led to the new field of plasmonics in which light transport along metal nanoparticle arrays and waveguides is studied at distances as small as a few nanometers (nm). At the same time, electronic structure calculations have also reached the nm size scale, so that the distinction between radiation and matter scale is being blurred out. This has led to a variety of studies where dipolar emission coupling of a few plasmons and excitons are considered, with interesting resonance, field- and spatial-dependence and more. Matter-radiation on the nanoscale (nanopolaritonics in short) is now ripe for a realistic description of both near-field radiation and molecules. The PI and his group are merging Maxwell's near-field description with modern studies of electronic dynamics, to simulate combined matter-radiation (plasmon-exciton, i.e., polariton) systems on the nanoscale. Some applications being considered are: gating of radiation transfer, specifically in large scale plasmonic systems with birefringence effects, including questions about whether molecules can control these systems, an application with possible use in imaging; nonlinear selective microscopy on the nanoscale -- a field with potentially huge impact for sensing applications from engineering to medicine; conversion of electromagnetic near-field energy to physical motion on the nanoscale, which will have practical importance in any field requiring motion control; photovoltaics where plasmons are hoped to reduce absorber sizes; matching of near and far fields, which could conceivably be affected by molecular motion; and the development of plasmon logic circuits .

Daniel Neuhauser of UCLA is supported by an award from the Chemical Theory, Models and Computational Methods program for work to develop a theoretical methodology to explore molecular nanopolaritonics with a large number of molecules. Molecular Nanopolaritonics intends to unify the treatment of radiation and matter on the nano scale. A previous award on this subject has introduced the concept of a unified treatment of matter and radiation on the nanoscale with arbitrary geometries and predicted that molecules will have large designed responses which can manipulate at will the transport of radiation in plasmon carrying structures. The present research unifies molecular and electromagnetic treatments on a larger scale through the development of theories that handle multitude of molecules with explicit time-dependent treatments and study the interaction with, and effects of, molecules and electromagnetic plasmons. The proposal tackles the difficult problem of embedding molecules directly on top of plasmon carrying structures, necessitating the development of multi-scale approaches that employ a detailed time-dependent orbital or density-matrix treatments in an inner region, supplemented by orbital-free or Maxwell studies on outer scales. The approaches use a time-dependent analogue of complex-Poisson descriptions, thereby significantly increasing the time-step of FDTD and making it commensurate with that of electronic dynamics. Further, new embedding techniques allow for designed orbital-free descriptions of plasmonics structures with the correct frequency response, thereby allowing large-scale embedding.

There are two disparate phenomena associated with radiation on the small scale. Metal structures support propagating plasmons, and molecules, whether few separate ones or large clusters, interact by dipole-induced fields. Nanopolaritonics is a recent name for the field which aims to unify the treatment. A well known direction is the effect on the molecules due to the interaction with the strong fields generated by the metal plasmons (which can be magnified by orders of magnitude in specific geometries, especially involving corners). However, Nanopolaritonics also includes the equally important and little-explored other direction, whereby molecules influence the propagation of plasmon waves. The PI with his group have shown in simulations that the effects are strong in both directions. At present they develop embedding approaches whereby adsorbed molecules are described quantum mechanically as well as the underlying adsorbing structure. Bigger regions are described by more approximate methods, such as orbital-free methods or Maxwell treatments, modified to concentrate on small scales. Applications of the methodology will be plenty: gating of plasmonics transport, sensing of individual molecules individually and through their effects on plasmons, non-linear phenomena and their effects on localized radiation transfer and absorption by adsorbed molecules. The most important feature is that this research unifies the two disparate fields of radiation and electronic dynamics, which taken together with realistic treatments, can exhibit novel physical features beyond perturbative or model-type treatments.

With support from the Chemical Measurement and Imaging Program, Professors Weiss and Neuhauser at the University of California-Los Angeles are developing a new imaging tool to measure local surface plasmon field intensity near nanometer-sized structures. It is known that sometimes when the incoming light illuminates a surface immobilized with small metal features, the electrons in the metal can oscillate back and forth together and form a "wave" ? the so called "surface plasmon". Surface plasmon is an important optical phenomenon and has been widely used in many real world applications, including the dark red color in medieval stained-glass windows that are seen in an old buildings ?the color comes from the visible light interacting with gold nanoparticles embedded in the glass. In order to better utilize the surface plasmon phenomenon, it is important to understand how it is distributed around imperfect nano-structures. Modern science advancement allows scientists to estimate the distribution of surface plasmon field intensity with computer simulation programs, but direct measurements of such field intensity, especially around imperfectly prepared nano-structures, are challenging and have not been fully realized. Professors Weiss and Neuhauser are developing a way to directly measure surface plasmon intensity near a small surface structure by monitoring the blinking rate of certain types of inorganic particles. This method would allow them to map the field intensity at a very high spatial resolution. It is also very fast and inexpensive as compared with other methods currently in development. During this 18-month grant period, both groups are focusing on (1) placing the inorganic particles around nanometer-sized features on a surface and (2) studying how the placement of these particles may be used to map the local EM field intensity. They are applying this imaging technique to study how molecules move near a surface or how a reaction happens on a metal nanoparticle. The graduate students in two groups are involved in both experimental and theoretical components of research. Both professors are also actively engaged in encouraging talented high school student to be enrolled in graduate programs, in particular from underrepresented minority groups.

The ability to simultaneously superresolve plasmonic field strengths over a large region is unique and desirable. Such approach will deepen the understanding of and control over plasmonic systems, and will broaden the impact of plasmonics. The novel probing technology Professors Weiss and Neuhauser are working uses the dependence of the blinking statistics in quantum dots on the electric field strength to resolve plasmonic field strengths well below the diffraction limit. The methods negate complications typical of localizing dipole emitters near a metallic nanostructure. A theoretical framework based on modeling of the quantum dots response with time-dependent density functional theory in deterministic or stochastic variants is also used to construct simplified building blocks. A computationally simplified building-blocks based modeling then allow simulations of a very large number of quantum dots and plasmonic structures simultaneously, mimicking the on-going experimental systems. By optimizing the theoretical and experimental tools developed here, the detailed electric field map of ~100x100 micrometer-squared size regions may be measured in quick succession. The imaging method, if successful, could benefit many applications that rely on the ability to measure field strengths below the diffraction limit, ranging from biology, to high speed integrated circuits, to optical computing. Additionally, the software developed for the experiments and for the theory studies provides an approachable tool for analyzing and predicting field strengths in heterogeneous regions. Professors Weiss and Neuhauser intend to disseminate the research tools developed to a broad community through freely available software packages.

NONTECHNICAL SUMMARY

The National Science Foundation and the United States -- Israel Binational Science Foundation (BSF) jointly support this collaboration between a US-based researcher and an Israel-based researcher. The NSF Divisions of Materials Research and Chemistry fund this award jointly. The award supports computational research and education on the mechanical and electronic properties of black phosphorene. Black phosphorene is a material composed of elemental phosphorous that has been discovered and synthesized only recently. It is very similar to graphene, it forms a two-dimensional sheet, but it offers a significant advantage in that it behaves as a semiconductor: it exhibits a sizeable energy gap while supporting at the same time high-mobility charge carriers. In addition, it turns out that the electronic properties of black phosphorene can be readily tuned by applying mechanical stress and other methods. Therefore, just as silicon emerged as an ideal material for three-dimensional electronics, black phosphorene seems to emerge as the ideal infrastructure material for two-dimensional electronics technology.

The principal goal of this project is to study, understand, and eventually predict the properties of black phosphorene and its derivatives using theoretical and computational methods. Because of the way two-dimensional black phosphorene responds to mechanical stresses and to chemical perturbations, studying its properties using conventional computational methods is a highly challenging task, requiring the simulation of exceedingly large systems. Therefore, the first challenge the project will need to overcome is to build a computational tool that tackles large electronic systems containing thousands of atoms, and apply it to the study of black phosphorene. This challenge can be met by using methodologies developed by the PIs that can generally be described as stochastic computational techniques. These approaches are akin to statistical methods used in polling, and make it possible to accurately simulate material properties for much larger systems than is possible with traditional, non-stochastic approaches. Once the tools are developed, the PIs will use them to study realistic two-dimensional black-phosphorene sheets, providing a theoretical framework for fundamental understanding and for guiding future experiments on this material.

The theoretical tools developed and used in this project will be made available to the community, with an aim to increase access to the developed methodology. The educational component of the project emphasizes the use of computational tools relevant for the research for the training and education of graduate students and postdoctoral fellows. Undergraduate and high school students will be involved in the research, especially in the running of large-scale simulations. All will benefit from close interactions with the Israeli collaborators.

TECHNICAL SUMMARY

The National Science Foundation and the United States -- Israel Binational Science Foundation (BSF) jointly support this collaboration between a US-based researcher and an Israel-based researcher. The NSF Divisions of Materials Research and Chemistry fund this award jointly. The award supports computational research and education on the mechanical and electronic properties of black phosphorene. Traditional large-scale simulations of these properties are prohibitively expensive either for accurate density functional theory with exact exchange (DFT), or for highly accurate electronic structure methods based on Green's function (GW). This project will explore hitherto inaccessible regimes using the stochastic formulations of traditional DFT and GW. The stochastic formulations replace some, or all of the multitude of summations over orbitals inherent in electronics structure methods with a stochastic sampling of combinations of these orbitals. The stochastic approaches are designed to calculate from first principles the atomic and electronic structure of systems containing 10,000 atoms or more. Sizes of that magnitude are necessary for establishing realistic environments, which enable the study of anisotropic properties. Such capability allows the construction of a theoretical framework for fundamental understanding of black phosphorene, which in turn will help in guiding experiments and synthetic efforts by pointing out possible directions to achieve desired properties.

The unique ability to accurately simulate large black-phosphorene systems allows the exploration of electronic structure under a variety of experimental conditions, which include temperature, strain, and optical excitation. Using a combination of stochastic DFT and Langevin dynamics, the structure and phonon dispersion curves of large, layered black-phosphorene nanoribbons and nanotubes will be investigated, with and without mechanical stress. The structure of defects and adsorbates on the surface and perimeters will be studied as well.

The theoretical tools developed and used in this project will be made available to the community, with an aim to increase access to the developed methodology. The educational component of the project emphasizes the use of computational tools relevant for the research for the training and education of graduate students and postdoctoral fellows. Undergraduate and high school students will be involved in the research, especially in the running of large-scale simulations. All will benefit from close interactions with the Israeli collaborators.

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professors Shimon Weiss and Daniel Neuhauser at University of California-Los Angeles are studying light-matter interaction at the nanoscale. Specifically, the study explores how light-emitting nanoparticles or molecules interact with metal nanostructures underneath. The gained knowledge could find applications in high resolution imaging in cells, high-speed integrated circuits, and quantum information science. Professors Weiss and Neuhauser work closely with graduate, undergraduate and high school students by providing them multidisciplinary training opportunities. They also plan to make their software broadly available to other scientists who are working on super resolution imaging.

Professors Weiss and Neuhauser merge super-resolution techniques, wide-field single photon detector, and multiscale simulations to understand the coupling strength of point emitters to plasmonic nanostructures. A novel probing technology is used to simultaneously resolve plasmonic structure and field strengths well below the diffraction limit, exploiting the dependence of the blinking statistics of quantum dots on the electric field strength for Stochastic Optical Fluctuation Imaging (SOFI). An additional layer of polarized excitation and emission is used to help understand emitter-metal coupling/scattering strengths in close proximity. They then plan to implement the method to solve the inverse problem, where structure and function can be simultaneously measured without any a priori knowledge of the underlying system.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.