Miguel Fuentes-Cabrera

Theoretical study of the ordered-vacancy semiconducting compound CdAl2Se4

We report results from first-principles density functional calculations of the structural, electronic, and vibrational properties of the semiconducting CdAl2Se4 compound. The defective chalcopyrite-like I phase and the spinel-like Fdm phases are considered. We find within the local density approximation (LDA) that the total energies of the I and the Fdm phases are virtually identical. Within the generalized gradient approximation, however, the ground-state structure is found to be I (in agreement with experiment), while the Fdm phase is a high-pressure phase that theoretically becomes stable at 3 GPa (4.5 GPa experimentally). The I phase is found to have a direct electronic band gap while the Fdm phase has an indirect band gap. A correction of the LDA band gap for I using a generalized density functional theory is in excellent agreement with measurements. The vibrational spectrum of the I structure at zero pressure and as a function of pressure is determined. Up to 23 GPa, no modes become soft.

Theoretical study of the structural, electronic and vibrational properties of CdIn2Te4

Abstract The structural, electronic and vibrational properties of the ordered-vacancy compound CdIn 2 Te 4 have been studied theoretically in three phases. They are the tetragonal I4 and I42m phases, and a potential high-pressure Fd3m phase. We found that: (i) the I4 and I42m phases were virtually identical in total energy; (ii) a high pressure phase transition from either tetragonal phase to the Fd3m phase was unlikely; and (iii) the tetragonal phases were semiconducting with a direct band gap, while the Fd3m phase was metallic. We calculated the Raman and IR modes for the I42m phase and compared these with experimental values.

Phase stability and pressure-induced semiconductor to metal transition in crystalline GeSe2

The structural and electronic properties of crystalline GeSe2 are studied using ab initio density functional theory. GeSe2 exists in a variety of phases; here eight phases, six previously synthesized and two hypothetical, are investigated within the local density approximation and the generalized gradient approximation (GGA). The results show that the GGA correctly describes the energetics of the GeSe2 even with variations in charge density of layer GeSe2 structures. The stability of the phases studied is discussed, and the possible phase transitions under pressure are predicted and compared to experiment. The electronic structure of GeSe2 confirms, for the first time, that the high-pressure CdI2-type phase is metallic which may produce the semiconductor to metal transition in the GeSe2 system under pressure.

Extrapolating dynamic leidenfrost principles to metallic nanodroplets on asymmetrically textured surfaces

In an effort to enhance our knowledge on how to control the movement of metallic nanodroplets, here we have used classical molecular dynamics simulations to investigate whether Cu nanostructures deposited on nanopillared substrates can be made to jump at desired angles. We find that such control is possible, especially for Cu nanostructures that are symmetric; for asymmetric nanostructures, however, control is more uncertain. The work presented here borrows ideas from two seemingly different fields, metallic droplets and water droplets in the dynamic Leidenfrost regime. Despite the differences in the respective systems, we find common ground in their behavior on nanostructured surfaces. Due to this, we suggest that the ongoing research in Leidenfrost droplets is a fertile area for scientists working on metallic nanodroplets.

Ab initio study of the vibrational and electronic properties ofCdGa2S4 and CdGa2Se4 under pressure

The vibrational spectra of CdGa2S4 and CdGa2Se4 under pressure were calculated with an ab initio technique and compared to the experimental results of Ursaki et al (Ursaki V V, Burlakov I I, Tiginyanu I M, Raptis Y S, Anastassakis E and Anedda A 1999 Phys. Rev. B 59 257). The comparison is good even though the conclusions are different. Ursaki et al concluded that CdGa2S4 and CdGa2Se4 are disordered under pressure while here these materials remained ordered. The pressure dependence of the band gap is calculated to help clarify whether or not the disordering is occurring.

Ab initiostudy of the vibrational and electronic properties of CdGa2S4and CdGa2Se4under pressure

The vibrational spectra of CdGa2S4 and CdGa2Se4 under pressure were calculated with an ab initio technique and compared to the experimental results of Ursaki et al (Ursaki V V, Burlakov I I, Tiginyanu I M, Raptis Y S, Anastassakis E and Anedda A 1999 Phys. Rev. B 59 257). The comparison is good even though the conclusions are different. Ursaki et al concluded that CdGa2S4 and CdGa2Se4 are disordered under pressure while here these materials remained ordered. The pressure dependence of the band gap is calculated to help clarify whether or not the disordering is occurring.