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exercises:2017_uzh_cp2k-tutorial:hybrid [2017/07/11 23:15] – gtocciexercises:2017_uzh_cp2k-tutorial:hybrid [2020/08/21 10:15] (current) – external edit 127.0.0.1
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 The purpose of this section is to explain how to perform hybrid functional calculations (or Hartree-Fock exchange, HFX) with CP2K in condensed phase systems. It is based on the developments described in [[doi>10.1021/ct900494g]] and [[doi>10.1063/1.2931945]], and its efficient extension (ADMM) described in [[doi>10.1021/ct1002225]]. The purpose of this section is to explain how to perform hybrid functional calculations (or Hartree-Fock exchange, HFX) with CP2K in condensed phase systems. It is based on the developments described in [[doi>10.1021/ct900494g]] and [[doi>10.1063/1.2931945]], and its efficient extension (ADMM) described in [[doi>10.1021/ct1002225]].
  
-Hartree-Fock exchange in CP2K is based on four center electron repulsion integrals (ERI), these are computed with an external library ([[http://sourceforge.net/projects/libint/|libint]]). To do these exercises, CP2K must be linked to this library.+Hartree-Fock exchange in CP2K is based on four center electron repulsion integrals (ERI), these are computed with an external library ([[http://sourceforge.net/projects/libint/|libint]]).
  
-This approach has a computational cost that depends strongly on the nature of the basis, unless combined with ADMM (see below), do not use MOLOPT basis sets with HFX. We use basis sets from ''HFX_BASIS'', which are suitable.+This approach has a computational cost that depends strongly on the nature of the basis. Unless combined with ADMM (see below), do not use MOLOPT basis sets with HFX. We use basis sets from ''HFX_BASIS'', which are suitable.
  
 This tutorial is also based on the ''GPW'' method and the calculations will be run using the GTH pseudopotentials. This tutorial is also based on the ''GPW'' method and the calculations will be run using the GTH pseudopotentials.
  
 <note> <note>
-Tutorial re-adapted from [[https://www.cp2k.org/exercises:2016_summer_school:hfx]] +Tutorial re-adapted from the [[https://www.cp2k.org/exercises:2016_summer_school:hfx| Tutorial on HFX and ADMM 2016 at KCL]] 
-For more info see also the slides from Joost VandeVondele [[https://www.cecam.org/upload/talk/presentation_5766.pdf]] +For more info see also the slides from Joost VandeVondele [[pdf>https://www.cecam.org/upload/talk/presentation_5766.pdf| presentation 2011]], Sanliang Ling [[pdf>https://www.cp2k.org/_media/events:2016_user_meeting:cp2k-uk-2016-ling.pdf | presentation 2016]] and 
-and Sanliang Ling [[https://www.cp2k.org/_media/events:2016_user_meeting:cp2k-uk-2016-ling.pdf]]+Matt Watkins [[https://mattatlincoln.github.io/cp2k_workshop_2017 | presentation 2017]]
 </note> </note>
  
 ===== Truncated Coulomb operator ===== ===== Truncated Coulomb operator =====
  
-To enable HFX in the condensed phase (described at the Gamma point only), CP2K employs a truncated Coulomb operator for the exchange part. The physical picture is that we do not want to have 'self-exchange interactions' of an electron with its image in neighboring unit cells. As a rule of thumb, the maximum range (truncation radius) is L/2 where L is the smallest edge of the unit cell. The convergence of the exchange energy is exponential wrt. this radius. Typically, 5-6A provides good results, but this depends on the nature of the system, i.e. the band gap or the range of the maximally localized Wannier orbitals.+To enable HFX in the condensed phase CP2K employs a truncated Coulomb operator for the exchange part. The physical picture is that we do not want to have 'self-exchange interactions' of an electron with its image in neighboring unit cells. As a rule of thumb, the maximum range (truncation radius) is L/2 where L is the smallest edge of the unit cell. The convergence of the exchange energy is exponential wrt. this radius. Typically, 5-6A provides good results, but this depends on the nature of the system, i.e. the band gap or the range of the maximally localized Wannier orbitals.
  
 ==== 1st task : GGA restart wfn ==== ==== 1st task : GGA restart wfn ====
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    ! various runtypes (energy, geo_opt, etc.) available.    ! various runtypes (energy, geo_opt, etc.) available.
    RUN_TYPE ENERGY    RUN_TYPE ENERGY
-   ! limit the runs to 5min +   ! amount of information printed to output
-   WALLTIME 1800 +
-   ! reduce the amount of IO+
    IOLEVEL  MEDIUM    IOLEVEL  MEDIUM
 &END GLOBAL &END GLOBAL
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          &E_DENSITY_CUBE OFF          &E_DENSITY_CUBE OFF
          &END E_DENSITY_CUBE          &END E_DENSITY_CUBE
-         ! compute eigenvalues and homo-lumo gap each 10nd MD step+         ! compute eigenvalues and homo-lumo gap 
          &MO_CUBES          &MO_CUBES
             NLUMO 4             NLUMO 4
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          SCF_GUESS ATOMIC ! can be used to RESTART an interrupted calculation          SCF_GUESS ATOMIC ! can be used to RESTART an interrupted calculation
          MAX_SCF 30          MAX_SCF 30
-         EPS_SCF 1.0E-6 ! accuracy of the SCF procedure typically 1.0E-6 - 1.0E-7+         EPS_SCF 1.0E-6 ! accuracy of the SCF procedure, for OT typically 1.0E-6 - 1.0E-7, for diagonalization may have to be smaller
          &OT          &OT
             ! an accurate preconditioner suitable also for larger systems             ! an accurate preconditioner suitable also for larger systems
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           ! important parameter to get stable HFX calcs (contributions to hfx smaller than EPS_SCHWARZ are not considered)           ! important parameter to get stable HFX calcs (contributions to hfx smaller than EPS_SCHWARZ are not considered)
           EPS_SCHWARZ 1.0E-6           EPS_SCHWARZ 1.0E-6
-          ! needs a good (GGA) initial guess (screening on density matrix elements)+          ! needs a good (GGA) initial guess  
 +          ! screening on the product between maximum of density matrix elements and ERI
           SCREEN_ON_INITIAL_P TRUE           SCREEN_ON_INITIAL_P TRUE
         &END         &END
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           ! for condensed phase systems           ! for condensed phase systems
           POTENTIAL_TYPE TRUNCATED           POTENTIAL_TYPE TRUNCATED
-          ! should be less than halve the cell +          ! should be less than half the cell 
-          CUTOFF_RADIUS  2.5+          CUTOFF_RADIUS  6.0
           ! data file needed with the truncated operator           ! data file needed with the truncated operator
           T_C_G_DATA ./t_c_g.dat           T_C_G_DATA ./t_c_g.dat
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 Topics: Topics:
   * ''EPS_PGF_ORB'' controls the sparse pattern of the overlap matrix, any contribution of the density matrix smaller than ''EPS_PGF_ORB'' is treated as zero;   * ''EPS_PGF_ORB'' controls the sparse pattern of the overlap matrix, any contribution of the density matrix smaller than ''EPS_PGF_ORB'' is treated as zero;
-  * ''EPS_SCHWARZ'' parameter for Schwarz screening, where contributions to HFX smaller than ''EPS_SCHWARZ'' treated as zero. Choose typically between $10^{-6} and 10^{-9}$;+  * ''EPS_SCHWARZ'' parameter for Schwarz screening, where contributions to HFX smaller than ''EPS_SCHWARZ'' treated as zero. Typical values range between $10^{-6} and 10^{-9}$;
   * ''SCREEN_ON_INITIAL_P'' uses the density matrix initially available to SCF and starts to use screening on that;   * ''SCREEN_ON_INITIAL_P'' uses the density matrix initially available to SCF and starts to use screening on that;
   * ''EPS_PGF_ORB'', ''EPS_SCHWARZ'', ''SCREEN_ON_INITIAL_P'' and ''EPS_FILTER_MATRIX'' are parameters to guarantee stable SCF.   * ''EPS_PGF_ORB'', ''EPS_SCHWARZ'', ''SCREEN_ON_INITIAL_P'' and ''EPS_FILTER_MATRIX'' are parameters to guarantee stable SCF.
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   * Look at the output where the HOMO-LUMO gap has been printed out. How does this compare to the GGA result?    * Look at the output where the HOMO-LUMO gap has been printed out. How does this compare to the GGA result? 
   * Adjust the fraction of exchange (modify the input in two places!) to 20% and/or 30%, how does this influence the gap ?   * Adjust the fraction of exchange (modify the input in two places!) to 20% and/or 30%, how does this influence the gap ?
-  * Most of the time in the SCF cycle is spent in the first step, while the other steps are much faster. Why do you think is that?+  * The most expensive part of the whole SCF cycle is represented by the first step, while the other steps are much faster. Why is that?
   * __Optional__ You can check if the SCF cycle is stable by decreasing the values of ''EPS_PGF_ORB'', ''EPS_FILTER_MATRIX'' as well as ''EPS_SCHWARZ''. Re-run the calculation and see how this affects the ''ENERGY''.   * __Optional__ You can check if the SCF cycle is stable by decreasing the values of ''EPS_PGF_ORB'', ''EPS_FILTER_MATRIX'' as well as ''EPS_SCHWARZ''. Re-run the calculation and see how this affects the ''ENERGY''.
   * __Optional__ CP2K tries to store the ERI in-core and avoid to calculate them at each SCF step. Especially for large systems that can be run on large HCP machines it is important to run in-core operation and fit the calculations of the ERI into memory. To see the effect of not having enough memory on the time for the ''SCF'' cycle, modify the tag of ''MAX_MEMORY'' to 40 and rerun the calculation. How do the timings compare with those where ''MAX_MEMORY'' was larger?   * __Optional__ CP2K tries to store the ERI in-core and avoid to calculate them at each SCF step. Especially for large systems that can be run on large HCP machines it is important to run in-core operation and fit the calculations of the ERI into memory. To see the effect of not having enough memory on the time for the ''SCF'' cycle, modify the tag of ''MAX_MEMORY'' to 40 and rerun the calculation. How do the timings compare with those where ''MAX_MEMORY'' was larger?
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 Rerun the single point energy calculation and note the band gap.  Rerun the single point energy calculation and note the band gap. 
   * Is such a short range sufficient to have a sizable effect on the band gap ?   * Is such a short range sufficient to have a sizable effect on the band gap ?
-  * is ''HFX_MEM_INFO| Number of cart. primitive ERI's calculated'' very different for calculations with 2.5 and 6.0A truncation radius?+  * is ''HFX_MEM_INFO| Number of cart. primitive ERI's calculated'' very different for calculations with 2.5 and 6.0A truncation radius? Remember to use the same cutoff radius under the ''&PBE_HOLE_T_C_LR'' and ''&INTERACTION_POTENTIAL'' sections.
  
 ===== Auxiliary Density Matrix Methods (ADMM) ===== ===== Auxiliary Density Matrix Methods (ADMM) =====
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   RUN_TYPE ENERGY   RUN_TYPE ENERGY
   ! limit the runs to 30min   ! limit the runs to 30min
-  WALLTIME 1800+  WALLTIME 1800 
   ! reduce the amount of IO   ! reduce the amount of IO
   IOLEVEL  MEDIUM    IOLEVEL  MEDIUM 
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     ! Charge and multiplicity     ! Charge and multiplicity
-    CHARGE 0 +    CHARGE 1 
-    MULTIPLICITY 1+    MULTIPLICITY 2
  
     &MGRID     &MGRID
exercises/2017_uzh_cp2k-tutorial/hybrid.1499814957.txt.gz · Last modified: 2020/08/21 10:15 (external edit)