Kent Milfeld

Quantum molecular dynamics in intense laser fields: Theory and applications to diatomic molecules

The quantum dynamics of vibration–rotation excitation in diatomic molecules in intense laser fields is investigated. The Floquet method is used in solving the equations‐of‐motion for a Hamiltonian explicitly time‐dependent. This method requires computation of the time‐displacement propagator only over the first optical cycle of the laser field, and is accomplished both numerically and with Magnus approximations. A number of features of single and multiphoton absorption in the LiH, CO, IBr, and HF molecules are studied as functions of the laser intensity and frequency. Average photon absorption spectra are studied with respect to power broadening, dynamic Stark shifts and line shapes. In some cases effective two‐state perturbative results accurately agree with the numerical results. In addition, rotational distributions in IBr following two‐photon absorption are found to have both thermal components for nonresonant states and structured nonthermal components for states nearly in resonance with the field. F...

Complex resonance eigenvalues by the lanczos recursion method

Abstract A complex (non-standard) Lanczos recursion method (LRM) is used to determine resonance positions and widths from a Hamiltonian by the complex coordinate method (CCM). When the initial Lanczos vector is an approximate resonance eigenvector (e.g. obtained by the Taylor-Hazi stabilization method) the resonance positions and widths of a N × N Hamiltonian matrix are obtained by the diagonalization of a much smaller m × m tridiagonal matrix ( m ⪡ N ). The combination of the complex LRM and CCM to determine complex resonance energies is well suited for large Hamiltonian matrices: providing faster execution and requiring less memory than standard methods. A numerical example is presented.

Laser-assisted chemical reactions: Semiclassical approach employing floquet and R-matrix theories

Abstract A general theory of laser-assisted reactions which includes multiphoton effects is presented. The scattering dynamics is determined by the quantal R -matrix formalism and the semiclassical radiation—complex interaction is described by non-perturbative Floquet theory. The theory is applied to a model collinear A + BC reaction in an IR laser field.

A Comparative Study of Application Performance and Scalability on the Intel Knights Landing Processor

Intel Knights Landing represents a qualitative change in the Many Integrated Core architecture. It represents a self-hosted option and includes a high speed integrated memory together with a two dimensional mesh used to interconnect the cores. This leads to a number of possible runtime configurations with different characteristics and implications in the performance of applications. This paper presents a study of the performance differences observed when using the three MCDRAM configurations available in combination with the three possible memory access or cluster modes. We analyze the effects that memory affinity and process pinning have on different applications. The Mantevo suite of mini applications and NAS Parallel Benchmarks are used to analyze the behavior of very different application kernels, from molecular dynamics to CFD mini-applications. Two full applications, the Weather Research and Forecast (WRF) application and a Lattice Boltzman Suite (LBS3D) are also analyzed in detail to complete the study and present scalability results of a variety of applications.

Optimizing the PCIT algorithm on stampede's Xeon and Xeon Phi processors for faster discovery of biological networks

The PCIT method is an important technique for detecting interactions between networks. The PCIT algorithm has been used in the biological context to infer complex regulatory mechanisms and interactions in genetic networks, in genome wide association studies, and in other similar problems. In this work, the PCIT algorithm is re-implemented with exemplary parallel, vector, I/O, memory and instruction optimizations for todays multi- and many-core architectures. The evolution and performance of the new code targets the processor architectures of the Stampede supercomputer, but will also benefit other architectures. The Stampede system consists of an Intel Xeon E5 processor base system with an innovative component comprised of Intel Xeon Phi Coprocessors. Optimized results and an analysis are presented for both the Xeon and the Xeon Phi.

Discovery of biological networks using an optimized partial correlation coefficient with information theory algorithm on Stampede's Xeon and Xeon Phi processors

The partial correlation coefficient with information theory (PCIT) method is an important technique for detecting interactions between networks. The PCIT algorithm has been used in the biological context to infer complex regulatory mechanisms and interactions in genetic networks, in genome wide association studies, and in other similar problems. In this work, the PCIT algorithm is re‐implemented with exemplary parallel, vector, input/output (I/O), memory, and instruction optimizations for todays multi‐core and many‐core architectures. The evolution and performance of the new code targets the processor architectures of the Stampede supercomputer but will also benefit other architectures. The Stampede system consists of an Intel Xeon E5 processor base system with an innovative component consist of Intel Xeon Phi Coprocessors. Optimized results and an analysis are presented for both the Xeon and the Xeon Phi. Copyright

Dynamics of eigenstate transitions induced by external fields: A new approach

We present a new general method to obtain the dynamics of molecular eigenstates perturbed by an external field. The method uses the Davidson algorithm and the recursive residue generation method (RRGM) to obtain molecular states and dynamic information, respectively. For sparse matrices, as many as 106 basis states can be used to represent the molecule’s Hamiltonian and its perturbation.

Quantum mechanical study of multiphoton excitation of the nonrotating OCS molecule

A quantum mechanical approach based upon Floquet theory is used to study IR multiphoton excitation of the nonrotating OCS molecule within the frequency and power range of the cw CO2 laser. Using a classical field interacting with a quantum molecule in the dipole approximation, the effects of laser frequency and power are investigated by computing long‐time average transition probabilities, total energy absorption, and time‐dependent probabilities. While multiphoton excitation is found to occur at the most intense CO2 laser line [P(24)], high‐order excitation dominates near the weaker P(16) line, some 10 cm−1 higher in photon energy. Also, various types of time averaging and approximate dipole interactions are investigated.

A new general R-matrix theory of collinear reactions and its application to the H + H2 reaction

A new general R-matrix theory of collinear reactions is developed by using the polar coordinate for the inner interaction region and the Cartesian coordinate for the two outer (reactants and products) asymptotic regions. The theory is applied to the collinear H + H2 exchange reaction.

amask: A Tool for Evaluating Affinity Masks in Many-Core Processors

Today’s multi- and many-core systems have NUMA nodes, sockets, tiles, cores, and Symmetric Multi-Threading (SMT) which may require complicated affinity settings to optimally map processes to processors. In many-core systems with hundreds of processors, evaluating the affinity of a single process by surveying a list of processor numbers is time consuming and error prone. Comparing two or more process affinities is even more troublesome. The amask tool displays all process affinities as an easy-to-read matrix of processor-ids versus ranks and/or thread-ids, allowing researchers to quickly confirm default settings and the effect of manipulating affinity, either before or during a parallel execution (through a stand-alone executable or API, respectively).