arXiv subjects

J. Trembly

Publications and source records attributed to J. Trembly.

3 recordsLinked to original sources

arXiv2023

Computer Simulation of Carbonization and Graphitization of Coal

This study describes computer simulations of carbonization and graphite formation, including the effects of hydrogen, nitrogen, oxygen, and sulfur. We introduce a novel technique to simulate carbonization, "Simulation of Thermal Emission of Atoms and Molecules (STEAM)," designed to elucidate the removal of volatiles and density variations in carbonization residue. The investigation extensively analyzes the functional groups that endure through high-temperature carbonization and examines the graphitization processes in carbon-rich materials containing non-carbon "impurity elements". The physical, vibrational, and electronic attributes of impure amorphous graphite are analyzed, and the impact of nitrogen on electronic conduction is investigated, revealing its substitutional integration into the sp$^2$ layered network.

cond-mat.mtrl-sci↗

arXiv2022

Formation of amorphous carbon multi-walled nanotubes from random initial configurations

Amorphous carbon nanotubes (a-CNT) with up to four walls and sizes ranging from 200 to 3200 atoms have been simulated, starting from initial random configurations and using the Gaussian Approximation Potential [Phys. Rev. B 95, 094203 (2017)]. The important variables (like density, height, and diameter) required to successfully simulate a-CNTs, were predicted with a machine learning random forest technique. The models were validated $\textit{ex post facto}$ using density functional codes. The a-CNT models ranged from 0.55 nm - 2 nm wide with an average inter-wall spacing of 0.31 nm. The topological defects in a-CNTs were discussed and new defect configurations were observed. The electronic density of states and localization in these phases were discussed and delocalized electrons in the $\pi$ subspace were identified as an important factor for inter-layer cohesion. Spatial projection of the electronic conductivity favors axial transport along connecting hexagons, while non-hexagonal parts of the network either hinder or bifurcate the electronic transport. A vibrational density of states was calculated and is potentially an experimentally testable fingerprint of the material and the appearance of a low-frequency radial breathing mode was discussed. The thermal conductivity at 300 K was calculated using the Green-Kubo formula.

cond-mat.mtrl-sci↗

arXiv2022

Simulation of multi-shell fullerenes using Machine-Learning Gaussian Approximation Potential

Multi-shell fullerenes "buckyonions" were simulated, starting from initially random configurations, using a density-functional-theory (DFT)-trained machine-learning carbon potential within the Gaussian Approximation Potential (ML-GAP) Framework [Volker L. Deringer and Gabor Csanyi, Phys. Rev. B 95, 094203 (2017)]. A large set of such fullerenes were obtained with sizes ranging from 60 ~ 3774 atoms. The buckyonions are formed by clustering and layering starts from the outermost shell and proceed inward. Inter-shell cohesion is partly due to interaction between delocalized $\pi$ electrons into the gallery. The energies of the models were validated ex post facto using density functional codes, VASP and SIESTA, revealing an energy difference within the range of 0.02 - 0.08 eV/atom after conjuagte gradient energy convergence of the models were achieved with both methods.

cond-mat.dis-nn↗