J. Karl Johnson
William Kepler Whiteford Professor
and NETL Faculty Fellow
Molecular Thermodynamics and
Computational Materials Science
PhD in Chemical Engineering, Cornell University, 1992
MS in Chemical Engineering, Brigham Young University, 1987
BS in Chemical Engineering, Brigham Young University, 1985
(412) 624-5644
Email: karlj@pitt.edu
Professor Johnson joined the faculty in 1995 after two years as a National Research
Council/National Academy of Sciences Research Associate at the Naval Research Laboratory. Dr.
Johnson's current research interests are focused on molecular thermodynamics, atomistic computer
simulations, and theories of complex systems. The ultimate goal of this work is to develop
engineering models for industrially important materials and processes. A realistic treatment of the
relevant physics is a key step in developing such models. Computer simulations are used as tools for
elucidating the essential interactions and developing accurate theories. Using computer modeling to
design new materials and to guide more expensive experimental efforts is becoming increasingly
important in academia and industry.
Fast Flow Through Nanotubes. See the Science Magazine Perspective article, Science 19 May 2006:
Science, 19 May 2006, 312, p. 969
Discovery of New Metal Hydrides. One of our recent papers,
"Using First Principles Calculations To Identify New Destabilized Metal Hydride Reactions for Reversible Hydrogen Storage", Phys. Chem. Chem. Phys., 9, 1438-1452 (2007),
was chosen by the editors of Science Magazine as one of their "Editors' Choice" articles. See Science, Volume 315, Number 5819, 23 March 2007, page 1638.
This paper was one of the ten most viewed articles for March, 2007, in the journal Phys. Chem. Chem. Phys.
Quantum Molecular Sieve.Tritium (red spheres) adsorbed inside a (3,6) carbon nanotube (blue atoms) at a
temperature of 20 K and low pressure. Under these conditions hydrogen is
excluded from the carbon nanotube.
The work from this paper,
was featured in Physical Review Focus.
Hydrogen Adsorption in Carbon Nanotubes.
Hydrgen gas adsorbed in an array of (10,10) carbon nanotubes. The hydrogen
inside the nanotubes and in the interstitial channels is at a much higher
density than that of the bulk gas.
Click here to see an animated gif of hydrogen adsorbed in an array of carbon nanotubes.
Click here for a Shockwave animation of the same thing.
Methane hydrate simulations. The above figure is a single hydrate cage containing a single
methane molecule. A molecular dynamics simulation illustrating dissociation of this small cage
can be downloaded here. (mpg file, 4.2 MB)
DNA adsorbed on a single-walled nanotube
This is a Dickerson dodecamer, d[CGCGAATTCGCG]2, adsorbed onto a
single-walled carbon nanotube in solution. The water molecules are not
shown.
Carbon monoxide adsorbing onto the silver (110) surface.
The first layer of CO molecules chemisorb to the surface and
remain fixed in place. As the coverage of CO increases a second
layer forms that is physisorbed with binding energies orders of
magnitude lower than the first layer. We show here a computer
simulation of physisorption using model potentials including the
electrostatic interaction between the fluid CO molecules and the
chemisorbed molecules on the Ag surface.
Hydrogen storage is a crucial problem for fuel cell vehicles. One of our molecular simulations of hydrogen adsorption in single walled carbon nanotubes was recently featured on the cover of Chemical & Engineering News (Vol. 80, No. 2, January 14, 2002) shown in this figure. Our ongoing projects involve simulating hydrogen adsorption with more realistic models and examining the effect of hydrogen spillover from catalytic particles.
Click here for an MPEG movie of hydrogen adsorbed on a nanotube array.
A very large AVI file (35 MB) of the simulation is here.
We have used high-level quantum mechanical methods to compute accurately the potential energy surface for molecules. Shown here is a plot of the H2-H2 potential energy surface holding the center of mass distance one of the three angles fixed. The potential energy surface was generated by coupled cluster [CCSD(T)] calculations extrapolated to the infinite basis set limit. The calculated pair potential accurately reproduces experimental second virial coefficient and molecular beam scattering data. [J. Chem. Phys. 113, 3480-3481 (2000)]
Acetone on graphite:
Computer simulations are often used to complement experimental studies in order to gain a detailed understanding of molecular-level phenomena. We have modeled acetone adsorption on the graphite basal plane surface and compared our results with experimental thermal desorption spectroscopy data. Shown here is a snapshot of the acetone graphite system. [Langmiur, 18, 2595-2600 (2002).]
Dr. Johnson is a Faculty Fellow at the National Energy Technology Laboratory
(NETL) working with the Computational Chemistry Research Group in the Chemistry and Surface Science Division. His work with NETL involves modeling adsorption and diffusion of gases on nanoporous sorbents, including metal organic framework materials and single walled carbon nanotubes. This work is performed in conjunction with experimental collaborators within the NETL Chemistry and Surface Science Division. Dr. Johnson is also involved with modeling of surface and diffusion processes on metal/ceramic composites, such as WC/Co and related systems.
The Pittsburgh Post-Gazette featured an article on nanotubes a few years ago. Read the article here.
Our work on hydrogen storage was featured on the cover of "Science in the 21st Century", a publication released from the Executive Office of the President of the United States and compiled under the direction of the National Science and Technology Council. Click here for an electronic copy of this publication (1.2 MB).
