Browsing by Author "Romero, A.H."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Effects of strong electron correlations and van der Waals interactions in the physical properties of bulk and 2D FeCl2
    (Cambridge University Press, 2026) Lopez-Moreno, S.; Tellez-Mora, A.; Mejia Lopez, Jose Felix; Hernandez-Vazquez, E.E.; Romero, A.H.; Moran-Lopez, J.L.
    © 2025 The AuthorsWe conducted a first-principles study of FeCl2, focusing on the significance of strong electron correlations using the GGA+U approximation and van der Waals (vdW) interactions to enhance the description of its physicochemical properties. Our results provide an excellent characterization of both the bulk CdCl2-type structure and the 2D phase 1T crystal structure. We found that both phases were elastically and dynamically stable, showing good agreement with the experimental data from IR, Raman, inelastic neutron scattering, and magnetic measurements. The impact of the FeCl2 dimensionality is discussed in detail. Additionally, we investigated the less-explored distorted 1T phase (1T’), where structural distortions introduce anisotropies that notably affect its properties. Moreover, our analysis of the magnon spectrum aligns with the recently characterized magnetic properties of the FM 1T phase. Simultaneously, magnetic anisotropy calculations revealed that the 1T’ configuration exhibits greater stability in the presence of an external magnetic field.
  • Thumbnail Image
    Item
  • No Thumbnail Available
    Item
    Is NMR the tool to characterize the structure of C20 isomers?
    (2002) Romero, A.H.; Sebastiani, D.; Ramírez, R.; Kiwi, M.
    We investigate the feasibility of using nuclear magnetic resonance (NMR) chemical shift calculations as a tool to provide structural information for C-20 fullerene type molecules. NMR chemical shifts are extremely sensitive to the local chemical environment of an atom, reflecting unambiguously its bond lengths and angles as well as its hybridization. Thus, they can distinguish between the different isomers that are candidates for the ground state of this molecule. We calculate the NMR shifts for several C-20 isomers and show that NMR constitutes a potential tool to discriminate and identify experimentally a particular C-20 molecular conformation, and also the level of theory which best describes the experimental structure. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Thumbnail Image
    Item
    Subsurface bonding of hydrogen in niobium: A molecular-dynamics study
    (1998) Romero, A.H.; Schuller, I.K.; Ramirez, R.
    Binding energy of hydrogen in a (100) niobium slab is investigated through molecular-dynamics simulations. We introduce a hydrogen-niobium interaction potential that contains an attractive as well as a repulsive part, which is valid for surface-diffusion calculations. Simulations for high and low temperatures (compared with theta(Debye)) are presented. For the former case, we found that the hydrogen diffuses in the slab with a diffusion coefficient in agreement with experiment, and in most cases it is trapped inside the slab for T less than or equal to 900 K. Close to room temperature, there is an enhancement of the hydrogen binding energy, which causes self-trapping close to the surface. [S0163-1829(98)07043-X].