arXiv subjects

T. A. Arias

Publications and source records attributed to T. A. Arias.

At least 37 records · Page 2Linked to original sources

arXiv2010

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

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. This analysis reveals design principles for the construction of ultrasensitive nanotube mass sensors: under tensions close to the elastic limit, intrinsic losses allow for \emph{single yoctogram} mass resolution at room temperature, while cooling opens the possibility of \emph{sub-yoctogram} mass resolution.

cond-mat.mes-hall↗

arXiv2009

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

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. Moreover, through direct comparison with experimental measurements of chemical strain, we place constraints on the possible defects present in oxygen-poor strontium titanate and introduce a conjecture regarding the nature of the predominant defect in strontium-poor stoichiometries in samples grown via pulsed laser deposition. Finally, during the review process, we learned of recent experimental data, from strontium titanate films deposited via molecular-beam epitaxy, that show good agreement with our calculated value of the chemical strain associated with strontium vacancies.

cond-mat.mtrl-sci↗

arXiv2009

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

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 \emph{exact} expression of the entropy of noninteracting molecules and thus provides an ideal starting point for the inclusion of complex inter-molecular interactions which depend on the \emph{orientation} of the interacting molecules. We show how an excess free-energy functional can be constructed to reproduce the following properties of water: the dielectric response; the experimental site-site correlation functions; the surface tension; the bulk modulus of the liquid and the variation of this modulus with pressure; the density of the liquid and the vapor phase; and liquid-vapor coexistence. As a demonstration, we present results for the application of this theory to the behavior of liquid water in a parallel plate capacitor. In particular, we make predictions for the dielectric response of water in the nonlinear regime, finding excellent agreement with known data.

cond-mat.soft↗

arXiv2009

Impact of octahedral rotations on Ruddlesden-Popper phases of antiferrodistortive perovskites

This work presents the most detailed and extensive theoretical study to date of the structural configurations of Ruddlesden-Popper (RP) phases in antiferrodistortive (AFD) perovskites and formulates a program of study which can be pursued for RP phases of any AFD perovskite system. We systematically investigate the effects of oxygen octahedral rotations on the energies of RP phases in AFD perovskites (A_n+1 B_n O_3n+1) for n = 1...30, providing asymptotic results for n --> infinity that give both the form of the interaction between stacking faults and the behavior of such stacking faults in isolation. We find an inverse-distance interaction between faults with a strength which varies by as much as a factor of two depending on the configuration of the octahedra. We find that the strength of this effect can be sufficient to (a) stabilize or destabilize the RP phase with respect to dissociation into the bulk perovskite and the bulk A-oxide and (b) affect the energy scales of the RP phase sufficiently to constrain the rotational states of the octahedra neighboring the stacking faults, even at temperatures where the octahedra in the bulk regions librate freely. Finally, we present evidence that the importance of the octahedral rotations can be understood in terms of changes in the distances between oxygen ions on opposing sides of the RP stacking faults.

cond-mat.mtrl-sci↗

arXiv2008

"Kohn-Shamification" of the classical density-functional theory of inhomogeneous polar molecular liquids with application to liquid hydrogen chloride

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. We also treat both the linear- and saturation- dielectric responses of polar systems, presenting liquid hydrogen chloride as a case study.

cond-mat.soft↗

arXiv2008

Cluster assimilation and collisional filtering on metal-oxide surfaces

We present the first ab initio molecular dynamics study of collisions between metal-oxide clusters and surfaces. The resulting trajectories reveal that the internal degrees of freedom of the cluster play a defining role in collision outcome. The phase space of incoming internal temperature and translational energy exhibits regions where the collision process itself ensures that each cluster which does not rebound from the surface assimilates seamlessly onto it upon impact. This filtering may explain recent observations of a "fast smoothing mechanism" during pulsed laser deposition.

cond-mat.mtrl-sci↗

arXiv2007

Joint density-functional theory for electronic structure of solvated systems

We introduce a new form of density functional theory for the {\em ab initio} description of electronic systems in contact with a molecular liquid environment. This theory rigorously joins an electron density-functional for the electrons of a solute with a classical density-functional theory for the liquid into a single variational principle for the free energy of the combined system. A simple approximate functional predicts, without any fitting of parameters to solvation data, solvation energies as well as state-of-the-art quantum-chemical cavity approaches, which require such fitting.

cond-mat.soft↗

arXiv2004

Ab initio theory of Cr$_2$O$_3$ surface chemistry in solution

Using a new form of density functional theory for the {\em ab initio} description of electronic systems in contact with a dielectric environment, we present the first detailed study of the impact of a solvent on the surface chemistry of Cr$_2$O$_3$, the passivating layer of stainless steel alloys. Compared to vacuum, we predict that the presence of water has little impact on the adsorption of chloride ions to the oxygen-terminated surface but a dramatic effect on the binding of hydrogen to that surface. These results indicate that the dielectric screening properties of water are important to the passivating effects of the oxygen-terminated surface.

cond-mat.soft↗

arXiv2004

Modelling a suspended nanotube oscillator

We present a general study of oscillations in suspended one-dimensional elastic systems clamped at each end, exploring a wide range of slack (excess length) and downward external forces. Our results apply directly to recent experiments in nanotube and silicon nanowire oscillators. We find the behavior to simplify in three well-defined regimes which we present in a dimensionless phase diagram. The frequencies of vibration of such systems are found to be extremely sensitive to slack.

cond-mat.mes-hall↗

arXiv2004

Ab initio mechanical response: internal friction and structure of divacancies in silicon

This letter introduces ab initio study of the full activation-volume tensor of crystalline defects as a means to make contact with mechanical response experiments. We present a theoretical framework for prediction of the internal friction associated with divacancy defects and give the first ab initio value for this quantity in silicon. Finally, making connection with defect alignment studies, we give the first unambiguous resolution of the debate surrounding ab initio verification of the ground-state structure of the defect.

cond-mat.mtrl-sci↗

arXiv2003

Electron-Phonon Scattering in Metallic Single-Walled Carbon Nanotubes

Electron scattering rates in metallic single-walled carbon nanotubes are studied using an atomic force microscope as an electrical probe. From the scaling of the resistance of the same nanotube with length in the low and high bias regimes, the mean free paths for both regimes are inferred. The observed scattering rates are consistent with calculations for acoustic phonon scattering at low biases and zone boundary/optical phonon scattering at high biases.

cond-mat.mes-hall↗

arXiv2003

Robust ab initio calculation of condensed matter: transparent convergence through semicardinal multiresolution analysis

We present the first wavelet-based all-electron density-functional calculations to include gradient corrections and the first in a solid. Direct comparison shows this approach to be unique in providing systematic ``transparent'' convergence, convergence with a priori prediction of errors, to beyond chemical (millihartree) accuracy. The method is ideal for exploration of materials under novel conditions where there is little experience with how traditional methods perform and for the development and use of chemically accurate density functionals, which demand reliable access to such precision.

cond-mat.mtrl-sci↗

arXiv2002

New ab initio approach for high pressure systems with application to a new high-pressure phase for boron: perturbative momentum-space potentials

Through the use of perturbation theory, in this work we develop a method which allows for a substantial reduction in the size of the plane-wave basis used in density-functional calculations. This method may be used for both pseudopotentials and all-electron calculations and is particularly beneficial in the latter case. In all cases, the approach has the advantage of allowing accurate predictions of transferability errors for any environment. Finally, this method can be easily implemented into conjugate gradient techniques and it is therefore computationally efficient. In this work, we apply this method to study high pressure phases of boron. We find that boron undergoes a phase transition from the icosahedral family to the alpha-orthorhombic structure, both of which are semiconducting. The alpha-orthorhombic structure has lower energy than traditional mono-atomic structures, which supports the assertion that the metallic, and hence superconducting phase, for boron is much more complicated than a simple mono-atomic crystal. Moreover, we argue that the beta-orthorhombic structure could be a candidate for the superconducting phase of boron.

cond-mat.mtrl-sci↗

arXiv2002

Ab initio and finite-temperature molecular dynamics studies of lattice resistance in tantalum

This manuscript explores the apparent discrepancy between experimental data and theoretical calculations of the lattice resistance of bcc tantalum. We present the first results for the temperature dependence of the Peierls stress in this system and the first ab initio calculation of the zero-temperature Peierls stress to employ periodic boundary conditions, which are those best suited to the study of metallic systems at the electron-structure level. Our ab initio value for the Peierls stress is over five times larger than current extrapolations of experimental lattice resistance to zero-temperature. Although we do find that the common techniques for such extrapolation indeed tend to underestimate the zero-temperature limit, the amount of the underestimation which we observe is only 10-20%, leaving open the possibility that mechanisms other than the simple Peierls stress are important in controlling the process of low temperature slip.

cond-mat.mtrl-sci↗

arXiv2002

Accurate hyperfine couplings for C59N

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 method implemented on top of a standard pseudopotential plane--wave density--functional framework, we compute significantly more accurate values for the Fermi contact interaction.

cond-mat.mtrl-sci↗

arXiv2002

Elasticity of nanometer-sized objects

We initiate the development of a theory of the elasticity of nanoscale objects based upon new physical concepts which remain properly defined on the nanoscale. This theory provides a powerful way of understanding nanoscale elasticity in terms of local group contributions and gives insight into the breakdown of standard continuum relations. We also give two applications. In the first, we show how to use the theory to derive a new relation between the bending and stretching properties of nanomechanical resonators and to prove that it is much more accurate than the continuum-based relations currently employed in present experimental analyses. In the second, we use the new approach to link features of the underlining electronic structure to the elastic response of a silicon nanoresonator.

cond-mat.mtrl-sci↗

arXiv2002

Multiresolution analysis for efficient, high precision all-electron density-functional calculations

Multiresolution analysis of electronic structure affords the opportunity to capture the full physics of atomic cores in a systematically improvable manner. Applying new techniques, we demonstrate for the first time that multiresolution analysis of all-electron calculations within density-functional theory can be carried out to high precision with a computational effort comparable to that of the corresponding plane-wave pseudopotential calculation, which neither captures the full core physics nor is systematically improvable. With this approach, we present calculations of paramagnetic core-level shifts where local density-functional theory is the sole uncontrolled approximation.

cond-mat↗

arXiv2001

Improved tensor-product expansions for the two-particle density matrix

We present a new density-matrix functional within the recently introduced framework for tensor-product expansions of the two-particle density matrix. It performs well both for the homogeneous electron gas as well as atoms. For the homogeneous electron gas, it performs significantly better than all previous density-matrix functionals, becoming very accurate for high densities and outperforming Hartree-Fock at metallic valence electron densities. For isolated atoms and ions, it is on a par with previous density-matrix functionals and generalized gradient approximations to density-functional theory. We also present analytic results for the correlation energy in the low density limit of the free electron gas for a broad class of such functionals.

cond-mat.mtrl-sci↗