18 research outputs found
Microscopic origins of charge transport in triphenylene systems
We study the effects of molecular ordering on charge transport at the mesoscale level in a layer of approximate to 9000 hexa-octyl-thio-triphenylene discotic mesogens with dimensions of approximate to 20 x 20 x 60 nm(3). Ordered (columnar) and disordered isotropic morphologies are obtained from a combination of atomistic and coarse-grained molecular-dynamics simulations. Electronic structure codes are used to find charge hopping rates at the microscopic level. Energetic disorder is included through the Thole model. Kinetic Monte Carlo simulations then predict charge mobilities. We reproduce the large increase in mobility in going from an isotropic to a columnar morphology. To understand how these mobilities depend on the morphology and hopping rates, we employ graph theory to analyze charge trajectories by representing the film as a charge-transport network. This approach allows us to identify spatial correlations of molecule pairs with high transfer rates. These pairs must be linked to ensure good transport characteristics or may otherwise act as traps. Our analysis is straightforward to implement and will be a useful tool in linking materials to device performance, for example, to investigate the influence of local inhomogeneities in the current density. Our mobility-field curves show an increasing mobility with field, as would be expected for an organic semiconductor
Microscopic origins of charge transport in triphenylene systems
We study the effects of molecular ordering on charge transport at the mesoscale level in a layer of approximate to 9000 hexa-octyl-thio-triphenylene discotic mesogens with dimensions of approximate to 20 x 20 x 60 nm(3). Ordered (columnar) and disordered isotropic morphologies are obtained from a combination of atomistic and coarse-grained molecular-dynamics simulations. Electronic structure codes are used to find charge hopping rates at the microscopic level. Energetic disorder is included through the Thole model. Kinetic Monte Carlo simulations then predict charge mobilities. We reproduce the large increase in mobility in going from an isotropic to a columnar morphology. To understand how these mobilities depend on the morphology and hopping rates, we employ graph theory to analyze charge trajectories by representing the film as a charge-transport network. This approach allows us to identify spatial correlations of molecule pairs with high transfer rates. These pairs must be linked to ensure good transport characteristics or may otherwise act as traps. Our analysis is straightforward to implement and will be a useful tool in linking materials to device performance, for example, to investigate the influence of local inhomogeneities in the current density. Our mobility-field curves show an increasing mobility with field, as would be expected for an organic semiconductor
Moltemplate: A Tool for Coarse-Grained Modeling of Complex Biological Matter and Soft Condensed Matter Physics
Coarse-grained models have long been considered indispensable tools in the investigation of biomolecular dynamics and assembly. However, the process of simulating such models is arduous because unconventional force fields and particle attributes are often needed, and some systems are not in thermal equilibrium. Although modern molecular dynamics programs are highly adaptable, software designed for preparing all-atom simulations typically makes restrictive assumptions about the nature of the particles and the forces acting on them. Consequently, the use of coarse-grained models has remained challenging. Moltemplate is a file format for storing coarse-grained molecular models and the forces that act on them, as well as a program that converts moltemplate files into input files for LAMMPS, a popular molecular dynamics engine. Moltemplate has broad scope and an emphasis on generality. It accommodates new kinds of forces as they are developed for LAMMPS, making moltemplate a popular tool with thousands of users in computational chemistry, materials science, and structural biology. To demonstrate its wide functionality, we provide examples of using moltemplate to prepare simulations of fluids using many-body forces, coarse-grained organic semiconductors, and the motor-driven supercoiling and condensation of an entire bacterial chromosome
3D to 2D reorganization of silver–thiol nanostructures, triggered by solvent vapor annealing
Metal–organic composites are of great interest for a wide range of applications. The control of their struc-ture remains a challenge, one of the problems being a complex interplay of covalent and supramolecularinteractions. This paper describes the self-assembly, thermal stability and phase transitions of orderedstructures of silver atoms and thiol molecules spanning from the molecular to the mesoscopic scale.Building blocks of molecularly defined clusters formed from 44 silver atoms, each particle coated by amonolayer of 30 thiol ligands, are used as ideal building blocks. By changing solvent and temperature it ispossible to tune the self-assembled 3D crystals of pristine nanoparticles or, conversely, 2D layered structures, with alternated stacks of Ag atoms and thiol monolayers. The study investigates morphological,chemical and structural stability of these materials between 25 and 300 °Cin situandex situat the nano-scale by combining optical and electronic spectroscopic and scattering techniques, scanning probemicroscopies and density-functional theory (DFT) calculations. The proposed wet-chemistry approach isrelatively cheap, easy to implement, and scalable, allowing the fabricated materials with tuned propertiesusing the same building blocks
Structural characterisation of supported Rh(CO)2/gam-Al2O3 catalysts by periodic DFT calculations
Microscopic structures of monodispersed rhodium dicarbonyl species chemisorbed on a ceramic metal-oxide support (?-alumina) have been obtained by density functional theory (DFT) calculations with periodic boundary conditions applied. Several minimum energy structures of species were obtained and their relative energies indicate that, in the most energetically stable geometry, the rhodium atom is coordinated in a square-planar environment and forms a four-membered Rh–O–Al–O ring, with one Al atom octahedrally coordinated. Another docking geometry, close lying in energy, also has a square-planar coordination for the rhodium atom and involves a six-membered Rh–O–Al–O–Al–O ring with one Al octahedrally coordinated and one Al tetrahedrally coordinated. Computed bond lengths were found to be in reasonable agreement with experimental bond lengths as determined by EXAFS spectroscopy. Theoretical Rh K-edge XANES spectra suggest that the pre-edge region probes electronic states localized on the RhI(CO)2 unit, while postedge features probe the electronic states arising from the RhI(CO)2 interaction with the support, which partly depends on the docking geometry of the RhI(CO)2 units.<br/
Development and testing of a compact basis set for use in effective core potential calculations on rhodium complexes
Structural Characterization of Supported Rh<sup>I</sup>(CO)<sub>2</sub>/γ-Al<sub>2</sub>O<sub>3</sub> Catalysts by Periodic DFT Calculations
Microscopic
structures of monodispersed rhodium dicarbonyl species
chemisorbed on a ceramic metal-oxide support (γ-alumina) have
been obtained by density functional theory (DFT) calculations with
periodic boundary conditions applied. Several minimum energy structures
of species were obtained and their relative energies indicate that,
in the most energetically stable geometry, the rhodium atom is coordinated
in a square-planar environment and forms a four-membered Rh–O–Al–O
ring, with one Al atom octahedrally coordinated. Another docking geometry,
close lying in energy, also has a square-planar coordination for the
rhodium atom and involves a six-membered Rh–O–Al–O–Al–O
ring with one Al octahedrally coordinated and one Al tetrahedrally
coordinated. Computed bond lengths were found to be in reasonable
agreement with experimental bond lengths as determined by EXAFS spectroscopy.
Theoretical Rh K-edge XANES spectra suggest that the pre-edge region
probes electronic states localized on the Rh<sup>I</sup>(CO)<sub>2</sub> unit, while postedge features probe the electronic states arising
from the Rh<sup>I</sup>(CO)<sub>2</sub> interaction with the support,
which partly depends on the docking geometry of the Rh<sup>I</sup>(CO)<sub>2</sub> units
Microscopic origins of charge transport in triphenylene systems
We study the effects of molecular ordering on charge transport at the mesoscale level in a layer of ≈9000 hexa-octyl-thio-triphenylene discotic mesogens with dimensions of ≈20×20×60nm3. Ordered (columnar) and disordered isotropic morphologies are obtained from a combination of atomistic and coarse-grained molecular-dynamics simulations. Electronic structure codes are used to find charge hopping rates at the microscopic level. Energetic disorder is included through the Thole model. Kinetic Monte Carlo simulations then predict charge mobilities. We reproduce the large increase in mobility in going from an isotropic to a columnar morphology. To understand how these mobilities depend on the morphology and hopping rates, we employ graph theory to analyze charge trajectories by representing the film as a charge-transport network. This approach allows us to identify spatial correlations of molecule pairs with high transfer rates. These pairs must be linked to ensure good transport characteristics or may otherwise act as traps. Our analysis is straightforward to implement and will be a useful tool in linking materials to device performance, for example, to investigate the influence of local inhomogeneities in the current density. Our mobility-field curves show an increasing mobility with field, as would be expected for an organic semiconductor
Structural Characterization of Supported Rh<sup>I</sup>(CO)<sub>2</sub>/γ-Al<sub>2</sub>O<sub>3</sub> Catalysts by Periodic DFT Calculations
Microscopic
structures of monodispersed rhodium dicarbonyl species
chemisorbed on a ceramic metal-oxide support (γ-alumina) have
been obtained by density functional theory (DFT) calculations with
periodic boundary conditions applied. Several minimum energy structures
of species were obtained and their relative energies indicate that,
in the most energetically stable geometry, the rhodium atom is coordinated
in a square-planar environment and forms a four-membered Rh–O–Al–O
ring, with one Al atom octahedrally coordinated. Another docking geometry,
close lying in energy, also has a square-planar coordination for the
rhodium atom and involves a six-membered Rh–O–Al–O–Al–O
ring with one Al octahedrally coordinated and one Al tetrahedrally
coordinated. Computed bond lengths were found to be in reasonable
agreement with experimental bond lengths as determined by EXAFS spectroscopy.
Theoretical Rh K-edge XANES spectra suggest that the pre-edge region
probes electronic states localized on the Rh<sup>I</sup>(CO)<sub>2</sub> unit, while postedge features probe the electronic states arising
from the Rh<sup>I</sup>(CO)<sub>2</sub> interaction with the support,
which partly depends on the docking geometry of the Rh<sup>I</sup>(CO)<sub>2</sub> units