Fast algorithms for the electronic structure analysis

Speaker: 

Lin Lin

Institution: 

Lawrence Berkeley National Lab

Time: 

Monday, April 29, 2013 - 4:00pm to 5:00pm

Location: 

RH 306

Kohn-Sham density functional theory (KSDFT) is the most widely used electronic structure theory for condensed matter systems. The standard method for solving KSDFT requires solving N eigenvectors for an O(N) * O(N) Kohn-Sham  Hamiltonian matrix, with N being the number of electrons in the system.  The computational cost for such procedure is expensive and scales as O(N^3).  We have developed pole expansion plus selected inversion (PEXSI) method, in which KSDFT is solved by evaluating the selected elements of the inverse of a series of sparse symmetric matrices, and the overall algorithm scales at most O(N^2) for all materials including metallic and insulating systems.  The PEXSI method can be used with orthogonal or nonorthogonal basis set, and the electron density, total energy, Helmholtz free energy and atomic force are calculated simultaneously and accurately without using the eigenvalues and eigenvectors.  Combined with atomic orbital basis functions, the PEXSI method can be applied to study the electronic structure of nanotube systems with more than 10,000 atoms with minimum basis set even with on single processor.  The recently developed parallel PEXSI method further allows the accurate treatment of layered graphene-like structure with  more than 20,000 atoms, and can be efficiently parallelized to more than 10,000 processors on leadership class machines.

CONSENSUS and FLOCKING in SELF-ALIGNMENT DYNAMICS

Speaker: 

Eitan Tadmor

Institution: 

University of Maryland, Mathematics

Time: 

Wednesday, June 5, 2013 - 4:00pm to 5:00pm

Host: 

Location: 

RH306

We discuss self-organized dynamics of agent-based models
with focus on a prototype model driven by non-symmetric self-alignment
introduced in [1].
Unconditional consensus and flocking emerge when the self-alignment is
driven by global interactions with a sufficiently slow decay rate.  In
more realistic models, however, the interaction of self-alignment is
compactly supported, and open questions arise regarding the emergence
of clusters/flocks/consensus, which are related to the propagation of
connectivity of the underlying graph.
In particular, we discuss heterophilious self-alignment: here, the
pairwise interaction between agents increases with the diversity of
their positions and we assert that this diversity enhances
flocking/consensus. The methodology carries over from agent-based to
kinetic and hydrodynamic descriptions.

[1] A new model for self-organized dynamics and its flocking behavior, J.
Stat. Physics 144(5) (2011) 923-947.
 

Math faculty and graduate student to be recognized at the 2013 Celebration of Teaching Ceremony

Congratulations to Math Department faculty members, Dr. Sarah Eichhorn and Dr. Rachel Lehman, and Math graduate student, May Mei! They will be recognized at the 19th annual Celebration of Teaching Ceremony. Sarah and Rachel have been awarded the 2013 Instructional Technology Innovation Award for their work with online courses.

A new PDE approach for large time behavior of Hamilton-Jacobi equations

Speaker: 

Hung Tran

Institution: 

University of Chicago

Time: 

Tuesday, April 23, 2013 - 3:00pm to 4:00pm

Host: 

Location: 

RH306

 

I will present a new PDE approach to obtain large time behavior
of Hamilton-Jacobi equations. This applies to usual Hamilton-Jacobi
equations, as well as the degenerate viscous cases, and weakly coupled
systems. The degenerate viscous case was an open problem in last 15 years.
This is the joint work with Cagnetti, Gomes, and Mitake.

Dynamical density functional theory: modelling sedimentation, pattern formation and other phenomena in colloidal suspensions

Speaker: 

Andrew Archer

Institution: 

Loughborough University

Time: 

Monday, March 25, 2013 - 4:00pm to 5:00pm

Host: 

Location: 

RH 306

 

Over the last few years, a number of dynamical density functional theories (DDFT)
have been developed for describing the dynamics of the one-body density of both
colloidal and atomic fluids. The DDFT is capable of describing the dynamics of the
fluid down to the scale of the individual fluid particles. DDFT is particularly
successful for colloidal fluids, for which one may assume that the particles have
stochastic equations of motion and from the resulting Fokker-Plank equation one is
able to derive the DDFT. I will give an overview of the DDFT and show applications
to various inhomogeneous fluid dynamical phenomena such as colloidal sedimentation
and evaporative dewetting of nanoparticle suspensions, which exhibit pattern
formation.

Global weak solution of the general Ericksen-Leslie system in dimension two

Speaker: 

Changyou Wang

Institution: 

University of Kentucky

Time: 

Tuesday, May 14, 2013 - 3:00pm to 4:00pm

Host: 

Location: 

306R

 

In this talk, I will discuss the existence of a unique global weak solution
to the general Ericksen-Leslie system in $R^2$, which is smooth away from possiblyfinite many singular times, for any initial data. This is a joint work with Jinrui Huang and Fanghua Lin.

 

Sensitivity Analysis, Uncertainty Quantification, & Stochastic Modeling of Complex Biological and Environmental Systems

Speaker: 

Guang Lin

Institution: 

Pacific Northwest National Laboratory

Time: 

Monday, April 15, 2013 - 4:00pm to 5:00pm

Host: 

Location: 

RH306

 
Experience suggests that uncertainties often play an important role in quantifying the performance of complex systems. Therefore, uncertainty needs to be treated as a core element in modeling, simulation and optimization of complex systems. In this talk, a new formulation for analyzing uncertainty sensitivity, quantifying uncertainty and visualizing uncertainty will be discussed. An integrated simulation framework will be presented that quantifies both numerical and modeling errors in an effort to establish “error bars” in CFD. In particular, stochastic formulations based on Galerkin and collacation versions of the generalized Polynomial Chaos (gPC) will be discussed. Additionally, we will present some effective new ways of dealing with this “curse of dimensionality”. Particularly, adaptive ANOVA decomposition, and some stochastic sensitivity analysis techniques will be discussed in some detail. Several specific examples on sensitivity analysis and predictive modeling of thrombin production in blood coagulation chemical reaction network, flow and transport in randomly heterogeneous porous media, random roughness problem, and uncertainty quantification in carbon sequestration will be presented to illustrate the main idea of our approach.
 
A mesoscale particle based numerical method, Dissipative Particle Dynamics (DPD) is employed to model the red blood cell (RBC) deformation. RBC’s have highly deformable viscoelastic membranes exhibiting complex rheological response and rich hydrodynamic behavior governed by special elastic and bending properties and by the external/internal fluid and membrane viscosities. We present a multiscale RBC model that is able to predict RBC mechanics, rheology, and dynamics in agreement with experiments. The dynamics of RBC’s in shear and Poiseuille flows is tested against experiments. 

 

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