Molecular Dynamics Studies of Diamondlike Amorphous Carbon

1994 ◽  
Vol 336 ◽  
Author(s):  
P. A. Fedders ◽  
D. A. Drabold
Keyword(s):  
Molecular Dynamics ◽  
Amorphous Carbon ◽  
First Principles ◽  
Structural Models ◽  
Theoretical Work ◽  
Vibrational Properties ◽  
Defect States ◽  
Amorphous Network ◽  
Molecular Dynamics Methods ◽  
Compare And Contrast

ABSTRACTFirst principles molecular dynamics methods are used to construct supercells for diamondlike Amorphous carbon, to study its properties, and to compare and contrast it with a-Si. As with recent lab fabricated material, these supercells contain no hydrogen. Several structural models are introduced and the topological, electronic, and vibrational properties are discussed. In particular, in spite of the presence of 3-fold coordinated sites and no hydrogenation, we have obtained a supercell sample that has a gap of about 2.5 eV containing no defect states. To our knowledge, ours is the only theoretical work that agrees with recent experiments in this respect. We explore the nature of defects in the Amorphous network and, in particular, the atomistic origin of the clean gap in unhydrogenated C but not in unhydrogenated Si.

Preparation, Structure, And Electronic Properties Of Amorphous Gaas By Tight-Binding Molecular Dynamics

1993 ◽  
Vol 321 ◽  
Author(s):  
C. Molteni ◽  
L. Colombo ◽  
L. Miglio
Keyword(s):  
Molecular Dynamics ◽  
First Principles ◽  
Large Scale ◽  
Tight Binding ◽  
Computer Experiment ◽  
Dynamics Simulation ◽  
First Principles Calculations ◽  
Amorphous Network ◽  
Large Scale Simulations

ABSTRACTWe investigate the short-range structural properties of a-GaAs as obtained in a computer experiment based on a tight-binding molecular dynamics simulation. The amorphous configuration is obtained by quenching a liquid sample well equilibrated at T=1600 K. A detailed characterization of the topology and defect distribution of the amorphous network is presented and discussed. The electronic structure of our sample is calculated as well. Finally, we discuss the reliability and transferability of the present computational scheme for large-scale simulations of compound semiconductor materials by comparing our results to first-principles calculations.

scholarly journals A Molecular Dynamics Study of a Photodynamic Sensitizer for Cancer Cells: Inclusion Complexes of γ-Cyclodextrins with C70

2019 ◽  
Vol 20 (19) ◽  
pp. 4831 ◽  
Author(s):  
Giuseppina Raffaini ◽  
Fabio Ganazzoli
Keyword(s):  
Molecular Dynamics ◽  
Cancer Therapy ◽  
Cancer Cells ◽  
Inclusion Complexes ◽  
Direct Injection ◽  
Theoretical Work ◽  
Stable Complex ◽  
Apolar Solvent ◽  
Molecular Dynamics Methods ◽  
The Stability

Photodynamic therapy is an emerging treatment of tumor diseases. The complexes with γ-cyclodextrins (γ-CD) and fullerenes or their derivatives can be used as photosensitizers by direct injection into cancer cells. Using molecular mechanics and molecular dynamics methods, the stability and the geometry of the 2:1 complexes [(γ-CD)2/C70] are investigated analyzing the differences with the analogous C60 complexes, studied in a previous theoretical work and experimentally found to be much less efficient in cancer therapy. The inclusion complex of γ-CD and C70 has a 2:1 stoichiometry, the same as C60, but is significantly less stable and displays an unlike arrangement. In vacuo, mimicking an apolar solvent, the complex is compact, whereas in water the two γ-CDs encapsulate C70 forming a relatively stable complex by interacting through their primary rims, however exposing part of C70 to the solvent. Other higher-energy complexes with the γ-CDs facing different rims can form in water, but in all cases part of the hydrophobic C70 surface remains exposed to water. The stability and arrangement of these peculiar amphiphilic inclusion complexes having non-covalent interactions in water can be an important key for cancer therapy to enhance both the solubilization and the fullerene insertion into liposomes or cell membranes.

FIRST PRINCIPLES MOLECULAR DYNAMICS INVOLVING EXCITED STATES AND NONADIABATIC TRANSITIONS

2002 ◽  
Vol 01 (02) ◽  
pp. 319-349 ◽  
Author(s):  
NIKOS L. DOLTSINIS ◽  
DOMINIK MARX
Keyword(s):  
Molecular Dynamics ◽  
Excited States ◽  
First Principles ◽  
Electronic Structure Theory ◽  
Structure Theory ◽  
Condensed Phases ◽  
Nonadiabatic Dynamics ◽  
Large Molecules ◽  
Nonadiabatic Transitions ◽  
Molecular Dynamics Methods

Extensions of traditional molecular dynamics to excited electronic states and non-Born–Oppenheimer dynamics are reviewed focusing on applicability to chemical reactions of large molecules, possibly in condensed phases. The latter imposes restrictions on both the level of accuracy of the underlying electronic structure theory and the treatment of nonadiabaticity. This review, therefore, exclusively deals with ab initio "on the fly" molecular dynamics methods. For the same reason, mainly mixed quantum-classical approaches to nonadiabatic dynamics are considered.

scholarly journals THEORETICAL STUDY OF Si and N ADSORPTION ON THE Si-TERMINATED SiC(001) SURFACE

1999 ◽  
Vol 06 (06) ◽  
pp. 1143-1150
Author(s):  
L. PIZZAGALLI ◽  
A. CATELLANI ◽  
G. GALLI ◽  
F. GYGI ◽  
A. BARATOFF
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
First Principles ◽  
Theoretical Study ◽  
Structural Models ◽  
Inert Substrate ◽  
Dynamics Simulations ◽  
First Principles Molecular Dynamics

We report the results of first principles molecular dynamics simulations of the adsorption of Si and N atoms on a Si-terminated p(2×1) SiC(001) surface. In particular, we discuss different structural models for the Si-rich (3×2) surface, and the adsorption of 1/8, 1/2 and 1 monolayer nitrogen on the p(2×1) surface. Our simulations show that a SiC(001)-p(2×1) surface covered by a nitrogen monolayer is an inert substrate which inhibits growth.

Molecular Dynamics Studies of Defect Motion in a-Si:H

1994 ◽  
Vol 336 ◽  
Author(s):  
P. A. Fedders
Keyword(s):  
Molecular Dynamics ◽  
Time Evolution ◽  
First Principles ◽  
Activation Energies ◽  
Dangling Bond ◽  
Dangling Bonds ◽  
Relaxation Effects ◽  
Molecular Dynamics Methods ◽  
First Principles Molecular Dynamics

ABSTRACTFirst principles molecular dynamics methods are used to study the motion of defects including dangling bonds and H. We study motion among H passivating dangling bonds, bond centered H, and tetrahedral H. We find that relaxation effects can reduce activation energies by up to one eV. Our studies also include the actual simulation of the time evolution of an a-Si:H system for several picosec. Here we observe the motion of a dangling bond over several hops and the motion of an H atom by means dangling bond exchange.

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