Electronic properties of 2D and 1D systems: Difference between revisions
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==Input set up for a low dimensional system:== | ==Input set up for a low dimensional system:== | ||
Now we want to deal with systems of reduced dimensionality, e.g. periodic in one or two dimension but isolated in the other directions: | Now we want to deal with systems of reduced dimensionality, e.g. periodic in one or two dimension but isolated in the other directions. This is accomplished by: | ||
* Isolating the system in the non-periodic dimension as seen in the | |||
'''K-points and Gamma sampling''' | |||
* The '''Brillouin zone''' of a infinitely large cell subject to PBC becomes a single point, '''Gamma'''. Because of this, even when using a large but finite cell, K-point sampling should not be used. This should not be relevant in terms of results (if it is, spurious interactions are present), but would result in a waste of computational resources. The so-called '''Gamma sampling''' should then be sued. | |||
* Moreover, in view of the Gamma sampling, wave functions can be taken to be real, leading to more memory and computational time savings. | |||
* In Quantum ESPRESSO one needs to set the following: | |||
K_POINTS automatic | |||
1 1 1 0 0 0 # for Gamma sampling using complex wavefunctions | |||
# deprecated, unless for testing or debugging | |||
==Exercises:== | ==Exercises:== | ||
===Exercise 1:=== | ===Exercise 1:=== | ||
Revision as of 08:52, 1 April 2021
Prev:LabQSM#Module 3: Low dimensional structures (6h)
Input set up for a low dimensional system:
Now we want to deal with systems of reduced dimensionality, e.g. periodic in one or two dimension but isolated in the other directions. This is accomplished by:
- Isolating the system in the non-periodic dimension as seen in the
K-points and Gamma sampling
- The Brillouin zone of a infinitely large cell subject to PBC becomes a single point, Gamma. Because of this, even when using a large but finite cell, K-point sampling should not be used. This should not be relevant in terms of results (if it is, spurious interactions are present), but would result in a waste of computational resources. The so-called Gamma sampling should then be sued.
- Moreover, in view of the Gamma sampling, wave functions can be taken to be real, leading to more memory and computational time savings.
- In Quantum ESPRESSO one needs to set the following:
K_POINTS automatic
1 1 1 0 0 0 # for Gamma sampling using complex wavefunctions
# deprecated, unless for testing or debugging