52 citations · 161 across the 17 of their papers we have counts for
18 papers
Lattice dynamics of disordered phases of silicon and spatially resolved computations of thermal conductivity
A. Gautam, C. Ugwumadu, L. A. M. Rosset +3
The lattice dynamics of disordered systems (amorphous solids, polymers and glasses) are often distinct from crystalline analogues. Examples include the "two-level systems" and the…
Real-Space Mapping of Electronic Conductivity in Complex Materials
C. Ugwumadu, D. A. Drabold, R. M. Tutchton
We introduce KuboMap, a real-space representation of electronic conductivity derived from the Kubo-Greenwood formula. KuboMap defines a nonnegative conductivity density whose spati…
A Defect-Free Model of Amorphous Silicon with Pristine Electronic Structure
Louise A. M. Rosset, Chinonso Ugwumadu, Stephen R. Elliott +2
Amorphous silicon (a-Si) is understood to be the canonical continuous random network material, ideally defined by fully fourfold coordination. Here, we show that a defect-free ('id…
Temperature dependence of electronic conductivity from ab initio thermal simulation
Ridwan Hussein, Chinonso Ugwumadu, Kishor Nepal +3
We present a temperature-dependent extension of the approximate electronic conductivity formula of Hindley and Mott that leverages time-averaged fluctuations of the electronic dens…
Electronic and thermal properties of the phase-change memory material, Ge2Sb2Te5, and results from spatially resolved transport calculations
Kishor Nepal, Aashish Gautam, Ridwan Hussein +4
We report new insights into the electronic, structural, and transport (heat and charge) properties of the phase-change memory material Ge2Sb2Te5. Using realistic structural models…
Spatially Local Estimates of the Thermal Conductivity of Materials
C. Ugwumadu, A. Gautam, Y. G. Lee +1
In this paper we describe a spatial decomposition of the thermal conductivity, what we name "site-projected thermal conductivity", a gauge of the thermal conduction activity at eac…
New models of clean and hydrogenated amorphous silicon surfaces
Kishor Nepal, Aashish Gautam, Chinonso Ugwumadu +1
We present new atomistic models of amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) surfaces. The a-Si model included 4096 atoms and was obtained using local or…
Site-projected Thermal Conductivity: Application to defects, interfaces, and homogeneously disordered materials
A. Gautam, Y. G. Lee, C. Ugwumadu +3
With the rapid advance of high-performance computing and electronic technologies, understanding thermal conductivity in materials has become increasingly important. This study pres…
Physical origin of enhanced electrical conduction in aluminum-graphene composites
K. Nepal, C. Ugwumadu, K. N. Subedi +2
The electronic and transport properties of aluminum-graphene composite materials were investigated using ab initio plane wave density functional theory. The interfacial structure i…
Electronic Conductivity in Metal-Graphene Composites: The Role of Disordered Carbon Structures, Defects, and Impurities
K. Nepal, C. Ugwumadu, A. Gautam +2
This paper explores the transport properties of aluminum-carbon composite material via ab initio methods. Interfacial and electronic dynamics of the aluminum-graphene interface str…
Improved Photocatalytic Performance via Air-Plasma Modification of Titanium Dioxide: Insights from Experimental and Simulation Investigation
C. Ugwumadu, I. Olaniyan, H. K. Jeong +1
Commercial titanium dioxide is successfully plasma-treated under ambient conditions for different time periods, leading to reduced crystallite size and the creation of oxygen vacan…
Understanding defects in amorphous silicon with million-atom simulations and machine learning
Joe D. Morrow, Chinonso Ugwumadu, David A. Drabold +3
The structure of amorphous silicon is widely thought of as a fourfold-connected random network, and yet it is defective atoms, with fewer or more than four bonds, that make it part…
Computer Simulation of Carbonization and Graphitization of Coal
C. Ugwumadu, R. Olson, N. L. Smith +4
This study describes computer simulations of carbonization and graphite formation, including the effects of hydrogen, nitrogen, oxygen, and sulfur. We introduce a novel technique t…
Electronic transport in copper-graphene composites
K. N. Subedi, K. Nepal, C. Ugwumadu +2
We investigate the electronic transport properties of copper-graphene composites using a density-functional framework. Conduction in composites by varying the interface distance of…
Formation of amorphous carbon multi-walled nanotubes from random initial configurations
C. Ugwumadu, R. Thapa, Y. Al-Majali +2
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 Gau…
Atomistic Nature of Amorphous Graphite
C. Ugwumadu, K. Nepal, R. Thapa +1
This paper focuses on the structural, electronic, and vibrational features of amorphous graphite [R. Thapa , Phys. Rev. Lett. 128, 236402 (2022)]. The structure o…
Simulation of multi-shell fullerenes using Machine-Learning Gaussian Approximation Potential
C. Ugwumadu, K. Nepal, R. Thapa +4
Multi-shell fullerenes "buckyonions" were simulated, starting from initially random configurations, using a density-functional-theory (DFT)-trained machine-learning carbon potentia…
Ab initio simulation of amorphous graphite
Rajendra Thapa, Chinonso Ugwumadu, Kishor Nepal +2
A disorder-order transition from amorphous carbon (aC) to layered amorphous graphene (LAG) has been predicted using ab-initio methods. Amorphous carbon at densities close to the gr…