RESUMO
An interatomic potential for sulfur has been developed using the bond order addition to the modified embedded-atom method (MEAM-BO). In order to correctly model the interaction between molecules, dispersion forces have been included via the DFT-D3 modification. It is demonstrated that this semiempirical classical potential correctly reproduces the behavior of the S2 dimer, various cyclic sulfur rings, the molecular solids α-, ß-, and γ-sulfur, and a number of theoretical, high symmetry sulfur structures. This potential will serve as a useful tool in the atomistic modeling of sulfur and, ultimately, in the modeling of sulfur containing organic compounds using this updated MEAM-BO formalism.
RESUMO
We report a fully electrical microcantilever device that utilizes capacitance for both actuation and detection and show that it can characterize various gases with a bare silicon microcantilever. We find the motion of the cantilever as it rings down when the oscillating force is removed, by measuring the voltage induced by the oscillating capacitance in the microcantilever∕counterelectrode system. The ringdown waveform was analyzed using an iterative numerical algorithm to calculate the oscillator motion, modeling the cantilever∕electrode capacitance to calculate the electrostatic force. We find that nonlinearity in the motion of the cantilever is not necessarily a disadvantage. After calibration, we simultaneously measure viscosity and density of several gaseous mixtures, yielding viscosities within ±2% and densities within ±6% of NIST values.
