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Publications

Joint time-dependent density-functional theory for excited states of electronic systems in solution

Cornell Affiliated Author(s)
Author
J. Lischner
Tomas Arias
Abstract

We present a joint time-dependent density-functional theory for the description of solute-solvent systems in time-dependent external potentials. Starting with the exact quantum-mechanical action functional for both electrons and nuclei, we systematically eliminate solvent degrees of freedom and thus arrive at coarse-grained action functionals that retain the highly accurate ab initio description for the solute and are, in principle, exact. This procedure allows us to examine approximations underlying popular embedding theories for excited states.

Journal
Physical Review B - Condensed Matter and Materials Physics
Date Published
Group (Lab)
Tomas Arias Group

Structural phase transitions in Ruddlesden-Popper phases of strontium titanate: Ab initio and modulated Ginzburg-Landau approaches

Cornell Affiliated Author(s)
Author
J. Lee
Tomas Arias
Abstract

We present a systematic ab initio study of antiferrodistortive (AFD) order in Ruddlesden-Popper (RP) phases of strontium titanate, Sr1+n Ti n O3n+1, as a function of both compressive epitaxial strain and phase number n. We find all RP phases to exhibit AFD order under a significant range of strains, recovering the AFD order of bulk SrTiO3 as ∼1/n2. A Ginzburg-Landau Hamiltonian including interoctahedral interactions reproduces our ab initio results well, opening a pathway to understanding other nanostructured perovskite systems. © 2010 The American Physical Society.

Journal
Physical Review B - Condensed Matter and Materials Physics
Date Published
Funding Source
0520404
Group (Lab)
Tomas Arias Group

Accelerating Correlated Quantum Chemistry Calculations Using Graphical Processing Units

Cornell Affiliated Author(s)
Author
M.A. Watson
R. Olivares-Amaya
R.G. Edgar
Tomas Arias
A. Aspuru-Guzik
Abstract

Graphical processing units are now being used with dramatic effect to accelerate quantum chemistry calculations. However, early work exposed challenges involving memory bottlenecks and insufficient numerical precision. This research effort addresses those issues, proposing two new tools for accelerating matrix multiplications of arbitrary size where single-precision accuracy is not enough. © 2010, IEEE. All rights reserved.

Journal
Computing in Science and Engineering
Date Published
Group (Lab)
Tomas Arias Group

Material limitations of carbon-nanotube inertial balances: Possibility of intrinsic yoctogram mass resolution at room temperature

Cornell Affiliated Author(s)
Author
J. Lischner
Tomas Arias
Abstract

We present a theoretical study of the intrinsic quality factor of the fundamental flexural vibration in a carbon nanotube and its dependence on temperature, radius, length, and tension. In particular, we examine three- and four-phonon decays of the fundamental flexural mode within quantized elasticity theory.

Journal
Physical Review B - Condensed Matter and Materials Physics
Date Published
Group (Lab)
Tomas Arias Group

Classical density-functional theory of inhomogeneous water including explicit molecular structure and nonlinear dielectric response

Cornell Affiliated Author(s)
Author
J. Lischner
Tomas Arias
Abstract

We present an accurate free-energy functional for liquid water written in terms of a set of effective potential fields in which fictitious noninteracting water molecules move. The functional contains an exact expression of the entropy of noninteracting molecules and thus provides an ideal starting point for the inclusion of complex intermolecular interactions which depend on the orientation of the interacting molecules.

Journal
Journal of Physical Chemistry B
Date Published
Funding Source
0113670
Group (Lab)
Tomas Arias Group

Elastic effects of vacancies in strontium titanate: Short- and long-range strain fields, elastic dipole tensors, and chemical strain

Cornell Affiliated Author(s)
Author
D.A. Freedman
D. Roundy
Tomas Arias
Abstract

We present a study of the local strain effects associated with vacancy defects in strontium titanate and report the first calculations of elastic dipole tensors and chemical strains for point defects in perovskites. The combination of local and long-range results will enable determination of x-ray scattering signatures that can be compared with experiments. We find that the oxygen vacancy possesses a special property-a highly anisotropic elastic dipole tensor which almost vanishes upon averaging over all possible defect orientations.

Journal
Physical Review B - Condensed Matter and Materials Physics
Date Published
Funding Source
0520404
Group (Lab)
Tomas Arias Group

Kohn-Sham-like approach toward a classical density-functional theory of inhomogeneous polar molecular liquids: An application to liquid hydrogen chloride

Cornell Affiliated Author(s)
Author
J. Lischner
Tomas Arias
Abstract

The Gordian knot of density-functional theories for classical molecular liquids remains finding an accurate free-energy functional in terms of the densities of the atomic sites of the molecules. Following Kohn and Sham, we show how to solve this problem by considering noninteracting molecules in a set of effective potentials. This shift in perspective leads to an accurate and computationally tractable description in terms of simple three-dimensional functions.

Journal
Physical Review Letters
Date Published
Group (Lab)
Tomas Arias Group

Accurate hyperfine couplings for C59N

Cornell Affiliated Author(s)
Author
G. Csányi
Tomas Arias
Abstract

We identify the shortcomings of existing ab initio quantum chemistry calculations for the hyperfine couplings in the recently characterized azafullerene, C59N. Standard gaussian basis sets in the context of all-electron calculations are insufficient to resolve the spin density near the cores of the atoms. Using the projector augmented wave (PAW) method implemented on top of a standard pseudo-potential plane-wave density-functional framework, we compute significantly more accurate values for the Fermi contact interaction. © 2002 Elsevier Science B.V. All rights reserved.

Journal
Chemical Physics Letters
Date Published
Group (Lab)
Tomas Arias Group

Elastic and anelastic behavior of materials in small dimensions

Cornell Affiliated Author(s)
Author
S.P. Baker
R.P. Vinci
Tomas Arias
Abstract

Under certain circumstances, decreasing the dimensions of a material may lead to elastic or anelastic properties that diverge from bulk behavior. A distinction is made between elastic deformation, for which bond rearrangements are not required, and anelastic behavior, which involves reversible deformation due to defect motion. Elastic deformation (due to bond stretching) remains structure-insensitive down to near-atomic length scales, and only small deviations are expected (of the order of 10%).

Journal
MRS Bulletin
Date Published
Group (Lab)
Tomas Arias Group

Accurate calculations of the Peierls stress in small periodic cells

Cornell Affiliated Author(s)
Author
D.E. Segall
Tomas Arias
A. Strachan
W.A. Goddard III
Abstract

The Peierls stress for a [111]-screw dislocation in bcc Tantalum is calculated using an embedded atom potential. More importantly, a method is presented which allows accurate calculations of the Peierls stress in the smallest periodic cells. This method can be easily applied to ab initio calculations, where only the smallest unit cells capable of containing a dislocation can be conviently used. The calculation specifically focuses on the case where the maximum resolved shear stress is along a 110-plane.

Journal
Journal of Computer-Aided Materials Design
Date Published
Group (Lab)
Tomas Arias Group