2 research outputs found
Probing Phase Transitions in Organic Crystals Using Atomistic MD Simulations
A profound understanding
of the physicochemical properties of organic
crystals is crucial for topics from material science to drug discovery.
Using molecular dynamics (MD) simulations with a sufficiently accurate
force field, microscopic insight into structure and dynamics can be
obtained of materials, including liquids and biomolecules. They are
a valuable complement to experimental investigations that are used
routinely in drug design, but not very often for studies of organic
crystals. Indeed, the often delicate interactions in organic crystals
act as a sensitive probe to investigate the accuracy of force fields.
Here, we study the structural, dynamic, and thermodynamic properties
of 30 organic crystals using the popular general AMBER force field
(GAFF). In particular, we investigate both solid–solid and
solid–liquid phase transitions. Melting points were determined
using extensive solid–liquid coexistence simulations. For many
compounds, we detect a phase transition from an ordered to a plastic
crystal in the simulations. Based on the translational and rotational
dynamics of the compounds, we can rationalize the properties of the
plastic crystal phase. MD simulations can therefore help to answer
the important question of whether or not organic crystals have a plastic
crystal phase, and if so, what are the underlying factors in the molecular
structure determining that
Electron Beam-Induced Writing of Nanoscale Iron Wires on a Functional Metal Oxide
Electron
beam-induced surface activation (EBISA) has been used
to grow wires of iron on rutile TiO<sub>2</sub>(110)-(1 × 1)
in ultrahigh vacuum. The wires have a width down to ∼20 nm
and hence have potential utility as interconnects on this dielectric
substrate. Wire formation was achieved using an electron beam from
a scanning electron microscope to activate the surface, which was
subsequently exposed to FeÂ(CO)<sub>5</sub>. On the basis of scanning
tunneling microscopy and Auger electron spectroscopy measurements,
the activation mechanism involves electron beam-induced surface reduction
and restructuring