Research Fields (current)

Noble Gas adsorption in quasicrystals surfaces (Al_73Ni_10Co_17)
Investigators: S. Curtarolo (Duke), W. Setyawan (Duke), R. Diehl (PSU), N. Ferralis (PSU), M. Cole (PSU).
Description. The discovery of quasicrystalline structures in 1984 changed the scientific community's view about crystals. The new structures were found to be aperiodic but still preserving a long-range order and to have symmetries forbidden by translational invariance (as 5-fold, 8-fold and 10-fold symmetry). As a result of this discovery, the IUCr commision on Aperiodic Crystals proposed a new definition in 1992: A crystal is any solid with an essentially discrete diffraction diagram; the symmetry of a crystal is implied by its diffraction image. However, the question of why do atoms form a complex, quasiperiodic pattern rather than a regularly-repeating crystal is still open. Besides this fundamental question, quasicrystals revealed other unexpected properties as high resistivity, low surface friction and stickiness, which are not yet clearly understood. This research explores the adsorption of noble gases on quasicrystal surfaces.


19. S. Curtarolo, W. Setyawan, R. D. Diehl, N. Ferralis, M. W. Cole, Evolution of order in Xe films on a quasicrystal surface, Phys. Rev. Lett. 95, 136104 (2005). [pdf]
We report results of the first computer simulation studies of a physically adsorbed gas on a quasicrystalline surface, Xe on decagonal Al-Ni-Co. The grand canonical Monte Carlo method is employed, using a semi-empirical gas-surface interaction, based on conventional combining rules, and the usual Lennard-Jones Xe-Xe interaction. The resulting adsorption isotherms and calculated structures are consistent with the results of LEED experimental data. The evolution of the bulk film begins in the second layer, while the low coverage behavior is epitaxial. This transition from epitaxial 5-fold to bulk-like 6-fold ordering is temperature dependent, occurring earlier (at lower coverage) for the higher temperatures.
ANIMATIONS
Animation of an adsorption isotherms at T=77K: isotherm_T77K_big.mpg. (big movie, 15MB), MPEG format.
Animation of an adsorption isotherms at T=77K: isotherm_T77K_small.mpg. (small movie, 4.5MB), MPEG format.
Animation of an experimental LEED isobar at P=1.6 10^-6 mbar isobar_experimental_LEED.mov. (6.9 MB), MOV format.
OTHER PUBLICATIONS IN THIS FIELD
23. W. Setyawan, N. Ferralis, R. D. Diehl, M. W. Cole, and S. Curtarolo, Xe films on a decagonal Al-Ni-Co quasicrystal surface, in preparation (2005).
22. R. D. Diehl, N. Ferralis, K. Pussi, M. W. Cole, W. Setyawan, and S. Curtarolo, The ordering of a Xe monolayer on a quasicristal Al-Ni-Co surface, in press Philosophical Magazine, (2005). [pdf]
ext. N. Ferralis, R. D. Diehl, K. Pussi, M. Lindroos, I. Fisher and C. J. Jenks, Low-energy Electron Diffraction Study of Xe Adsorption on the Ten-fold Decagonal Al-Ni-Co Quasicrystal Surface, Phys. Rev. B 69, 075410 (2004). [pdf]
ext. N. Ferralis, K. Pussi, M. Gierer, E. J. Cox, J. Ledieu, I. Fisher, C. J. Jenks, M. Lindroos, R. McGrath and R. D. Diehl, Structure of the ten-fold d-Al-Ni-Co quasicrystal surface, Phys. Rev. B 69, 153404 (2004). [pdf]

High-Throughput ab-initio computing: transition-metal binary alloysext. ont>
Investigators: S. Curtarolo (Duke), D. Morgan (MIT), G. Ceder (MIT).
Description. We have developed the technology for high-throughput quantum computing in materials. The first stage of the research is the investigation of a transition-metal binary alloys.
All the calculations are available here http://datamine.mit.edu (with Chris Fischer).

Data Mining of Ab-initio Quantum Calculations
Investigators: S. Curtarolo (Duke), D. Morgan (MIT), K. Persson (MIT), J. Rodgers (Toth Inc.), G. Ceder (MIT).
Description. Predicting and characterizing the crystal structure of materials is a key problem in materials research and development. It is typically addressed with highly accurate quantum mechanical computations on a small set of candidate structures, or with empirical rules that have been extracted from a large amount of experimental information, but have limited predictive power. In this research, we transfer the concept of heuristic rule extraction to a large library of ab-initio calculated information, and demonstrate that this can be developed into a tool for crystal structure prediction. We propose a new approach whereby ab-initio investigations on new systems are informed with knowledge obtained from results already collected on other systems. We refer to this approach as Data Mining of Quantum Calculations (DMQC), and demonstrate its efficiency in increasing the speed of predicting the crystal structure of new and unknown materials. Using a Principal Component Analysis on over 6000+ ab-initio energy calculations, we show that the energies of different crystal structures in binary alloys are strongly correlated between different chemical systems, and demonstrate how this correlation can be used to accelerate the prediction of new systems. We believe that this is an interesting new direction to address in a practical manner the problem of predicting the structure of materials.

Hydrogen Adsorption in Carbon Nanostructures for Fuel Storage
Investigators: S. Curtarolo (Duke), J. Glass (Duke), C. Parker (Duke).
Description. TBA.

Multiscale dynamics of fast and ultrafast phenomena
Investigators: S. Curtarolo (Duke), G. Ceder (MIT).
Description. During the last decade revolutionary experimental advances allowing manipulations of atoms, precise growth processes, and investigation of defects in solids, pioneered the introduction of nanotechnology. Ab-initio atomistic calculations cannot span the size of nanostructures, and continuum macroscopic models do not offer the fine description necessary to investigate nanostructures. This is the area where multiscale modeling becomes the appropriate and fundamental tool to win the novel and outstanding theoretical challenges. In the static regime, multiscale modeling has been developed with great success in the framework of the quasicontinuum model. Unfortunately the extension to dynamics, multiple time-scales, and thermodynamics has been recognized as a non trivial problem. One attempt has been made by ourself [PRL2002] for the case of slow dynamics, where thermodynamical properties are conserved by construction.
To create a multiscale environment, it is necessary to remove degrees of freedom of atoms: positions and momenta. As an extreme example, thermodynamics is a complete removal of such degrees of freedom, which is done through the construction of the partition function, and hence thermodynamical potentials. In this way, collective effects of position and momenta become volume and pressure. A multiscale framework is quite different from thermodynamics, since we want to remove only a subset of all the degrees of freedom. For instance, if we consider a finite one - dimensional chain of atoms that interact through nearest neighbor pair potentials, it is possible to remove every second atom, just considering each of these atoms, as part of a local system with its own local partition function. The local degrees of freedom can be removed by integrating over all the possible configurations of the particular atom. This integration produces a local partition function, and hence a local free energy and local entropy, which is nothing more than the information that is removed from the system, locally. With this construction, second neighbors become first neighbors connected with an effective potential, which is the microscopic analogy of the pressure for thermodynamic systems. The procedure can be iterated, and then, a complete multiscale description of the system is built. As this thermodynamic approach is rigorously correct in the equilibrium regime, its extension to slow dynamics is approximate.
In this research area, we are developing the theoretical framework for dynamical simulation of fast and ultrafast phenomena in multiscale systems. The problem is related to the construction of proper velocity-dependent potentials which reproduce thermodynamical properties in the long time frame. The solution of this problem will lead to a formidable tool to investigate phenomena in nanostructures, for instance: shocks, cracks, fractures, lubricity, and dynamics of phase transitions in materials in presence of defects and/or impurities. As an example, in the lubricity area, I intend to study the mechanism leading to energy dissipation between nano-contacts, and, using the multiscale formalism, compare the microscopic mechanism with the macroscopic behavior. For this application, multiscale fast-dynamics is the key tool the describe how the mechanical vibrations, caused by the atomic-size shear, couple their energies with local entropy production, creating heat production and transfer.