arXiv subjects

Roman Martoňák

Publications and source records attributed to Roman Martoňák.

20 records · Page 2Linked to original sources

arXiv2013

Structure change, layer sliding, and metallization in high-pressure MoS$_{2}$

Based on ab initio calculations and metadynamics simulations, we predict that 2H-MoS$_2$, a layered insulator, will metallize under pressures in excess of 20-30 GPa. In the same pressure range, simulations and enthalpy optimization predict a structural transition. Free mutual sliding of layers takes place at this transition, the original 2H$_c$ stacking changing to a 2H$_a$ stacking typical of 2H-NbSe$_2$, an event explaining for the first time previously mysterious X-ray diffraction and Raman spectroscopy data. Phonon and electron phonon calculations suggest that pristine MoS$_2$, once metallized, will require ultrahigh pressures in order to develop superconductivity.

cond-mat.mtrl-sci↗

arXiv2012

Superhard sp3 carbon allotropes with odd and even ring topologies

Four sp3 carbon allotropes with six, eight, and 16 atoms per primitive cell have been derived using a combination of metadynamics simulations and topological scan. A chiral orthorhombic phase oC16 (C2221) was found to be harder than monoclinic M-carbon and shows excellent stability in the high-pressure range. A second orthorhombic phase of Cmmm symmetry, by \sim 0.028 eV/atom energetically lower than W-carbon, can be formed from graphite at \sim 9 GPa. In general, the mechanical response under pressure was found to depend on the structure topology, which reflects the way rings are formed from an initial graphene layer stacking.

cond-mat.mtrl-sci↗