## Research Activity: Condensed Matter Theory

Division: Materials Sciences and Engineering

Primary Contact(s): Dale Koelling (<Dale.Koelling@science.doe.gov> ,
301-903-2187)

Team Leader: Harriet Kung (Acting)

Division Director: Harriet Kung

**Portfolio** **Description:**

The Condensed Matter Theory activity supports basic research in theory,
modeling, and simulations complementing the experimental effort. A
current major thrust is in nanoscale science where links between the
electronic, optical, mechanical, and magnetic properties of
nanostructures and their size, shape, topology, and composition are
poorly understood. Other research areas include correlated behavior of
two dimensional electron gases, quantum transport, superconductivity,
magnetism, and optics. An important facilitating component is the
Computational Materials Science Network (CMSN) which enables groups of
scientists from Department of Energy (DOE) national laboratories,
universities, and (to a lesser extent) industry to address materials
problems requiring larger-scale collaboration across disciplinary and
organizational boundaries.

**Unique Aspects:**

New areas of materials science are being identified and studied. New
technology is enabling a much closer examination of the existing ones.
This healthy progress dictates that new theories be developed and that
established ones be reexamined and possibly extended. A very important
contribution of the theorist is enforcing a rational, consistent
understanding of experimental observations so that we can go forward.
Often, this involves working out implications of a theory for a specific
material or situation. In materials, this can be an extremely difficult
task owing to the very many atoms involved. Theorists have developed
many conceptual tools such as quasiparticles, entities defined to
examine phenomena at different length scales, or summary statistical
approaches to deal with this problem. Further development of such
conceptual tools continues to be a very important aspect within this
theoretical program. However, for many phenomena now being studied,
large scale computation must be used to perform the complex calculations
dictated by the fundamental theory or to perform the simulations of
systems with many interacting components. The rapid advance in
computational capabilities now enables research at such a level of
sophistication that computational science has become a "third way of
doing science," albeit, at a price. The complexity of such research
often dictates larger groups of collaborating researchers from a
diversity of disciplines and one response is CMSN. At present, CMSN
consists of six sub-projects: Excited States and Response Functions
(testing the accuracy of current levels of fundamental theory);
Microstructural Effects on the Mechanics of Materials (computational
study of the fundamental basics of metallurgy); Fundamentals of Dirty
Interfaces: From Atoms to Alloy Microstructures (the development of
microstructure in heterogeneous materials); Magnetic Materials Bridging
Basic and Applied Science (an attempt to interconnect different scales
of magnetic behavior from quantum mechanical electronic behavior all the
way to continuum micro-mechanical properties); Predictive Capability for
Strongly Correlated Systems (an attempt to advance capabilities in many
body theory); and Multiscale Studies of the Formation and Stability of
Surface-Based Nanostructures.

**Relationship to Other** **Programs:**

This activity interacts with all the other research activities within
the BES Materials Science and Engineering Division, driven by mutual
interest. Because production supercomputer resources used by the
division are administered in this activity, there is an enhanced
awareness of opportunity. Within the Office of Science, frequent
interaction occurs with the [Mathematical, Information, and
Computational Sciences Division](http://www.science.doe.gov/ascr/mics/).
Information on university grants is shared with the National Science
Foundation (NSF), peer reviews are sometimes shared, and on occasion
there is joint funding of grants. On the international level
participation in organizing and steering committees is frequent, as are
exchanges of experts between foreign and domestic institutions.

**Significant Accomplishments:**

Consistent with an emphasis on nanoscience, notable achievements in this
area have been made within this activity. Research into low dimensional
materials has revealed exciting new information and has pointed to new
possibilities in creating new tailored materials and devices. Highlights
include:

-   By judiciously attaching molecules to nanoclusters, one can guide
    them to assemble in a specified manner. (The rule book remains to be
    written, but it is under construction.)

-   Gold nanoparticles behave much more like their platinum group
    neighbors in the periodic table including exhibiting interesting
    catalytic behavior. When passivated by dodecane thiols, they can
    self-assemble into nanocrystalline superlattices with unique
    properties.

-   Nanocrystalline diamond can form with a bucky ball-like surface
    reconstruction. The carbon nanoparticles exhibit very weak quantum
    confinement unlike silicon and germanium.

-   Silicon nanotubes can be formed by stabilization with a core of
    nickel atoms. Unlike carbon, silicon nanotubes are not stable
    without such help.

Significant progress has also been made in other areas as illustrated by
the following examples:

-   

-   Dynamic mean-field theory, which is exact for infinite dimensions,
    has been successfully coupled with three dimensional band theory.
    The resulting hybrid theory has been used to elucidate the spin
    polarization of CrO~2~-- a famous magnetic recording material that
    might find new use in spintronics. A competition between
    quasiparticle behavior and local-moment behavior is found.

-   

-   

-   

-   

-   Progress has been made on the question of how to treat core-hole
    effects in x-ray absorption spectra by a collaboratory research team
    of the CMSN. The team, which focuses on Excited States and Response
    Functions, brought together experts of all applicable approaches to
    compare approaches and elucidate the formal relationships among
    them. What resulted was an excellent prescription for success but
    with identified places for improvement. This is needed not only for
    fundamental understanding of the details of x-ray absorption
    phenomena but for technological applications, e.g. the measurement
    of the thickness of integrated circuit interconnects.

-   The origin of the light-induced conductivity in the transparent
    oxide 12CaO·7Al~2~O~3~ is traced to electrons excited off hydrogen H
    ions present. To accomplish this, it was first necessary to
    accomplish calculating the Coulomb gap leading to hopping
    conductivity.

-   A way has been found to see diffraction data for molecules adsorbed
    on surfaces. The conventional methods of low energy electron
    diffraction will not work; the molecules produce no Bragg spots
    because they are randomly distributed on the surface. However, it
    has been shown that the information is present in the intensity
    variation of the spots originating from the substrate. The resulting
    technique has successfully revealed the geometry of small
    hydrocarbons on a palladium surface.

**Mission Relevance:**

The program's ultimate purpose is to understand the properties of
existing materials and to reveal new ones that are more efficient in
producing, storing, and using energy. To this end, the programs in this
portfolio have the common goal of achieving a basic understanding of
matter at all scales ranging from atomic to bulk. The experimental and
theoretical programs work closely together, but there are also more
independent modes of research. The theorists try to establish a
theoretical basis for experimentally observed results, which almost
always suggests further experiments, and thus leads to new results. New
experiments and experimental techniques are suggested. New science is
also produced by simulating processes on computers. "Computer
experiments" can be performed which are difficult or impossible to
perform in the laboratory. They are also much easier to dissect and to
vary the conditions in order to isolate the effective mechanisms. For
example, the behavior of the surface layers of materials sliding on each
other and a new understanding of the role of lubricants has been
obtained in this way. Other examples include investigations into the
behavior of electrons flowing in nano wires and nanotubes and in the
properties of matter at extreme conditions of temperature and pressure.

**Scientific Challenges:**

The close relationship between the experimental and theoretical programs
dictates that many challenges are common to both. Examples are exploring
the behavior of complex systems, investigating nano-scale systems, and
understanding superconductivity. New ways of conceptually visualizing
and characterizing phenomena will broaden our horizons. Stripes
occurring in cuprate superconductors and two dimensional electron gasses
are excellent examples. Bridging length scales is a major thrust. The
tactic of dividing up the effects in materials according to the length
scale at which they occur has greatly facilitated our understanding. But
for theorists, this creates the problem of how to pass needed
information between the different constructs used at the different
length scales. Only in that way can one calculate parameters rather than
make phenomenological fits. Such is the basis for improved understanding
and greater precision of our modeling. It is a continuing major goal on
which limited progress has been made. Bridging time scales is similarly
important, but far less progress has been made. Basic theory
improvements are also needed. For example, density functional theory is
our most computationally tractable many body theory, but it defines many
functionals both for the ground state or ensemble energy and separately
for the properties that must be determined. Whereas knowledge of the
exchange-correlation functional for the ground state energy is
reasonably advanced, knowledge of all other functionals is still quite
rudimentary. Other many body approaches, although far more
computationally intensive, provide important information and require
further development. Improvements are also needed in our computational
tools. Materials theory is a very heavy consumer of computer resources
even if not so visibly as other disciplines. (This is because materials
theory deals with many dissimilar problems rather than a few overarching
ones.) The materials community could make very productive use of vast
increases in computational capability. Because the phenomenal growth due
to hardware improvements is actually overshadowed by those due to clever
algorithm design, further improvements in "tool development" will
significantly impact future development of science in a qualitative way.

**Funding Summary:**

Dollars in Thousands

[FY 2005]{.underline} [FY 2006]{.underline} [FY 2007]{.underline}
[Request]{.underline}

19,798 22,888 27,408

> [Performer]{.underline} [Funding Percentage]{.underline}
>
> DOE Laboratories 56%
>
> Universities 44%

The program provides funding for 65 university grants supporting about
as many students and partially supporting about 64 faculty and senior
staff. There are approximately 70 postdoctoral associates fully or
partially supported by this activity. The program supports research at
Lawrence Berkeley National Laboratory, Brookhaven National Laboratory,
Ames Laboratory, Argonne National Laboratory, Oak Ridge National
Laboratory, Los Alamos National Laboratory, Lawrence Livermore National
Laboratory, and National Renewable Energy Laboratory. Programs at the
national laboratories are multi-investigator efforts on problems that
require extensive participation by experimental and theoretical
scientists. Many of the research efforts at national laboratories
involve interfaces with the university and industrial communities and
with user facilities. Additionally, about \$1.68M is provided for
projects of the CMSN.

**Projected Evolution:**

Materials will be modeled with ever-greater sophistication, realism, and
complexity. Needs and opportunities will drive the effort inexorably in
this direction. Science at the nanoscale will continue a major thrust,
although it is only one of many. A cooperative effort between the BES
Chemical Sciences, Geosciences, and Biosciences Division and the
[Mathematical, Information, and Computational Sciences
Division](http://www.science.doe.gov/ascr/mics/) seeks to enhance our
capabilities to model and simulate at the nanoscale. The CMSN will be
enhanced to bring together teams adequate to address the more complex
problems envisioned. Large scale computing will continue to be an
important aspect of the research, but a new balance will have to be
achieved in the allocation of resources, which will impact all BES
activities.