Theoretical work establishes structural stability of nanoscale diamond structures

Robert A. Freitas Jr. (2009 Feynman Prize in Nanotechnology for Theory) writes:

I just put up a link to a DMS (diamondoid mechanosynthesis) paper of mine that was published about 6 months ago. It’s my second published paper with our Russian collaborators (we already have a third one in press and a fourth one in prep) and is now available online:

Denis Tarasov, Ekaterina Izotova, Diana Alisheva, Natalia Akberova, Robert A. Freitas Jr., “Structural Stability of Clean, Passivated, and Partially Dehydrogenated Cuboid and Octahedral Nanodiamonds up to 2 Nanometers in Size,” J. Comput. Theor. Nanosci. 8(February 2011):147-167;

In sum, the paper reports that small hydrogenated diamond cubes and octahedra of the type that might serve as nanoparts in diamondoid molecular machinery are structurally stable. This stability is retained even under various conditions of partial dehydrogenation of the nanopart surfaces — such conditions as would exist on the faces of intermediate structures that would arise during (almost) atom-by-atom fabrication of these nanoparts via DMS.

ABSTRACT. The use of precisely applied mechanical forces to induce site-specific chemical transformations is called positional mechanosynthesis, and diamond is an important early target for achieving mechanosynthesis experimentally. The next major experimental milestone may be the mechanosynthetic fabrication of atomically precise 3D structures, creating readily accessible diamond-based nanomechanical components engineered to form desired architectures possessing superlative mechanical strength, stiffness, and strength-to-weight ratio. To help motivate this future experimental work, the present paper addresses the basic stability of the simplest nanoscale diamond structures — cubes and octahedra — possessing clean, hydrogenated, or partially hydrogenated surfaces. Computational studies using Density Functional Theory (DFT) with the Car-Parrinello Molecular Dynamics (CPMD) code, consuming ~1,466,852.53 CPU-hours of runtime on the IBM Blue Gene/P supercomputer (23 TFlops), confirmed that fully hydrogenated nanodiamonds up to 2 nm (~900-1800 atoms) in size having only C(111) faces (octahedrons) or only C(110) and C(100) faces (cuboids) maintain stable sp3 hybridization. Fully dehydrogenated cuboid nanodiamonds above 1 nm retain the diamond lattice pattern, but smaller dehydrogenated cuboids and dehydrogenated octahedron nanodiamonds up to 2 nm reconstruct to bucky-diamond or onion-like carbon (OLC). At least three adjacent passivating H atoms may be removed, even from the most graphitization-prone C(111) face, without reconstruction of the underlying diamond lattice.

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