Difference between revisions of "Electronic properties of 2D and 1D systems"

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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:
 
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  
+
* Isolating the system in the non-periodic dimension as seen in [[Electronic properties of isolated molecules]], so inserting an amount of vacuum in the supercell.
 +
* Sampling the Brillouin zone that now has reduced dimension:
  
−
 
+
In Quantum ESPRESSO one needs to set the following:
−
'''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
 
   K_POINTS automatic
−
   1 1 1  0 0 0        # for Gamma sampling using complex wavefunctions
+
   nk nk 1  0 0 0        # for Gamma sampling using complex wavefunctions
 
                         # deprecated, unless for testing or debugging
 
                         # deprecated, unless for testing or debugging
 +
this will generate a 2D sampling
  
 
==Exercises:==
 
==Exercises:==
 
===Exercise 1:===
 
===Exercise 1:===

Revision as of 10:56, 1 April 2021

Picture by AlexanderAlUS - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=11294534

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 Electronic properties of isolated molecules, so inserting an amount of vacuum in the supercell.
  • Sampling the Brillouin zone that now has reduced dimension:

In Quantum ESPRESSO one needs to set the following: 

  K_POINTS automatic
  nk nk 1   0 0 0         # for Gamma sampling using complex wavefunctions
                        # deprecated, unless for testing or debugging

this will generate a 2D sampling

Exercises:

Exercise 1:

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