Exploring the vibrational properties of anharmonic crystals – Mark Johnson (Theory of Condensed Matter)

December 2, 2020 @ 11:30 am – 12:30 pm
Angela Harper

Calculating the electronic properties of crystals is now routine, and
many software packages are available for performing these calculations.
In contrast, calculations of the vibrational properties of crystals are
far less developed. When vibrational properties are not neglected
entirely, they are typically calculated under the harmonic
approximation. The harmonic approximation makes calculation relatively
straightforward and inexpensive, but for many systems this approximation
is overly restrictive, and there are many crystal properties which it
entirely fails to capture.

There are a number of anharmonic vibrational methods which are widely
used for calculating the properties of molecular systems, and in recent
years some of these methods have been adapted for use with crystals.
However, crystals are not molecules. Unlike molecules, crystals have
translational symmetry, and many crystals have complex space group
symmetries. Further, crystals are extended systems, and so their
properties must be correctly extensive or intensive. Symmetry and
size-consistency can be exploited to accelerate crystal models, and any
model which violates these conditions is likely to be inaccurate, yet
these conditions are not widely recognised in the vibrational modelling

This talk seeks to highlight the importance of symmetry and
size-consistency to modelling the vibrational properties of crystals,
and to present a number of problems with existing models which arise
where these constraints are broken.

Join Zoom Meeting: https://bham-ac-uk.zoom.us/j/85702415099?pwd=VTh5aFZ4Sm9Nc1dxZXYwelJpc1JtZz09

Meeting ID: 857 0241 5099

Passcode: 501623

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