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exercises:2014_ethz_mmm:tio2_gap [2014/04/10 12:52]
oschuett
exercises:2014_ethz_mmm:tio2_gap [2020/08/21 10:15] (current)
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 ====== TiO$_2$ Band Gap as a function of %hfx ====== ====== TiO$_2$ Band Gap as a function of %hfx ======
  
-One problem with standard DFT is that correlation effects can lead to errors in evaluating certain system properties, such as the band gap of semiconductors. More information can be found here: \\ +One problem with standard DFT is that correlation effects can lead to errors in evaluating certain system properties, such as the band gap of semiconductors. More information can be found here: [[doi>10.1126/science.1158722]]
-A common approach to correct for electronic self-interaction is the //ad hoc/mixing of a fraction of the exact Hartree-Fock exchange\\+
  
-The goal of this exercise is to identify the needed amount of exact Hartree-Fock exchange (%hfx) to correctly reproduce the anatase TiO$_2$ experimental band gap (3.2 eV). \\ +A common approach to correct for electronic self-interaction is the //ad hoc// mixing of a fraction of the exact Hartree-Fock exchange. The goal of this exercise is to identify the needed amount of exact Hartree-Fock exchange (%hfx) to correctly reproduce the anatase TiO$_2$ experimental band gap (3.2 eV). To do so, you will need to run at least 4 single point calculations on bulk TiO$_2$ with varying amount of exact exchange.  
- + 
-To do so, you will need to run at least 4 single point calculations on bulk TiO$_2$ with varying amount of exact exchange. \\ +
 Report the result as follows: Report the result as follows:
 ^%hfx^E$_{gap}$^ ^%hfx^E$_{gap}$^
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 | 10 | ... | | 10 | ... |
 | .. | ... | | .. | ... |
-Then plot E$_{gap}$  as a function of %hfx. \\  +Then plot E$_{gap}$  as a function of %hfx. By interpolating the data on the plot, the needed amount of hfx to correctly reproduce the experimental band gap can be determined.
-By interpolating the data on the plot, the needed amount of hfx to correctly reproduce the experimental band gap can be determined.+
  
-<note tip> Hybrid calculations can be fairly expensive (~N$^4$). You should run on 16 nodes.  </note> +<note tip> 
-<note tip> To furhter decrease the cost of the calculation, you can restart from previously generated wavwefunction files (*-RESTART.wfn). One is already made available for you here: </note>+Hybrid calculations can be fairly expensive, because they scale with $\mathcal{O}(N^4)$Therefore, you should run these jobs on 16 nodes. To further decrease the cost of the calculation, you can restart from previously generated wave-function files (*-RESTART.wfn). At the end of this exercise, a readily optimized wave-function is provided to you
 +</note>
  
 ===== Questions ===== ===== Questions =====
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 ===== Required files ===== ===== Required files =====
-  * file with truncation parameters: {{:exercise:t_c_g.dat.gz|}} +==== Parameters for Truncated Coulomb Potential ==== 
-  Restart wavefunction, useful to speed up calculations: {{:exercise:tio2_pbe-restart.wfn.gz|}}+{{t_c_g.dat.gz| Download here}} 
 +   
 +==== Restart wave-function ==== 
 + This is useful to speed up the calculation 
 + {{tio2_pbe-restart.wfn.gz| Download here}}
  
 <note> These files are compressed with gzip. To unpack them run: <note> These files are compressed with gzip. To unpack them run:
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 </note> </note>
  
-  * input file+==== Input File ====
 <code - anatase_25hfx.inp> <code - anatase_25hfx.inp>
  
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   METHOD Quickstep   METHOD Quickstep
   &DFT   &DFT
-   ! external data-files for basis-set, pseudo-potentials and wavefunction to restart from+   ! external data-files for basis-set, pseudo-potentials and wave-function to restart from
    BASIS_SET_FILE_NAME ./BASIS_TiO    BASIS_SET_FILE_NAME ./BASIS_TiO
    POTENTIAL_FILE_NAME ./POTENTIALS_TiO    POTENTIAL_FILE_NAME ./POTENTIALS_TiO
    RESTART_FILE_NAME   ./pbe-RESTART.wfn    RESTART_FILE_NAME   ./pbe-RESTART.wfn
        
-    &MGRID              ! section required to deinfe the cutoff of the grids in the program+    &MGRID              ! section required to define the cutoff of the grids in the program
       CUTOFF 400        ! for this system the default value is too small        CUTOFF 400        ! for this system the default value is too small 
     &END MGRID          ! and can lead to non-physical results     &END MGRID          ! and can lead to non-physical results
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     &END     &END
          
-    &SCF                   ! ensures convergence of the scf cycle+    &SCF                   ! ensures convergence of the SCF cycle
       EPS_SCF 1.0E-6               EPS_SCF 1.0E-6        
-      SCF_GUESS RESTART    ! here we specify to restart from an external wavefunction (name specified above)+      SCF_GUESS RESTART    ! here we specify to restart from an external wave-function (name specified above)
       MAX_SCF 40       MAX_SCF 40
       &OUTER_SCF       &OUTER_SCF
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       &HF       &HF
         FRACTION 0.25         ! this is the hfx section. The amount of hfx must be consistent with above         FRACTION 0.25         ! this is the hfx section. The amount of hfx must be consistent with above
-        &SCREENING            ! Screening of the electronic repulstion up to the given threshold. This section is needed+        &SCREENING            ! Screening of the electronic repulsion up to the given threshold. This section is needed
           EPS_SCHWARZ 1.0E-6           EPS_SCHWARZ 1.0E-6
-          SCREEN_ON_INITIAL_P TRUE  ! having an external wavefunction, a preliminary screening+          SCREEN_ON_INITIAL_P TRUE  ! having an external wave-function, a preliminary screening
         &END                        ! can be performed to speed up calculations         &END                        ! can be performed to speed up calculations
         &MEMORY         &MEMORY
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             COORD_FILE_NAME tio.cif               COORD_FILE_NAME tio.cif  
     &END     &END
-    &KIND O                          ! external basis and pseudopotentials for Ti and O +    &KIND O                          ! external basis and pseudo-potentials for Ti and O 
       BASIS_SET cpFIT3       BASIS_SET cpFIT3
       POTENTIAL GTH-PBE-q6       POTENTIAL GTH-PBE-q6
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 </code> </code>
  
- +==== Basis Set ==== 
-  * basis set +<code - BASIS_TiO>
-<code - BASIS_TiO >+
  
 # O # O
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 </code> </code>
  
-  * potential+==== Pseudo-Potential ====
 <code - POTENTIALS_TiO> <code - POTENTIALS_TiO>
 # #
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 </code> </code>
  
-  * anatase *.cif file (cristallographic information file = anatse crystal strucutre)+==== Anatse Crystal Structure ==== 
 + 
 +''.cif'' = crystallographic information file
  
-<code - tio.cif >+<code - tio.cif>
 #====================================================================== #======================================================================
  
exercises/2014_ethz_mmm/tio2_gap.1397134327.txt.gz · Last modified: 2020/08/21 10:14 (external edit)