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exercises:2017_uzh_cp2k-tutorial:gw

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exercises:2017_uzh_cp2k-tutorial:gw [2017/07/04 08:00] – [5. Cubic-scaling GW calculations] jwilhelmexercises:2017_uzh_cp2k-tutorial:gw [2022/10/31 14:33] (current) – oschuett
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 +<note warning>This text is out of date. Please use [[howto:gw | this howto]] instead.</note>
 +
 ====== GW method for computing electronic levels ====== ====== GW method for computing electronic levels ======
  
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 For periodic GW calculations, a special correction scheme is necessary. A similar problem is appearing in Hartree-Fock calculations. In HF, an easy way out is given by the truncation of the Coulomb operator which works due to the convenient form of the HF equations. GW does not exhibit this convenient form and therefore, this truncation does not work for GW calculations. The theory why a correction is necessary and the correction scheme is described in [[doi>10.1103/PhysRevB.95.235123]] [7]. For periodic GW calculations, a special correction scheme is necessary. A similar problem is appearing in Hartree-Fock calculations. In HF, an easy way out is given by the truncation of the Coulomb operator which works due to the convenient form of the HF equations. GW does not exhibit this convenient form and therefore, this truncation does not work for GW calculations. The theory why a correction is necessary and the correction scheme is described in [[doi>10.1103/PhysRevB.95.235123]] [7].
  
-The basis can be found in {{exercises:2017_uzh_cp2k-tutorial:LiH_BASIS_RI.tar ?direct&400 |}}. Then run the calculation as listed below. The computed gap of LiH with the input from below should be 5.95 eV which is still significantly off from the converged result of 4.7 eV from [[doi>10.1103/PhysRevB.95.235123]] [7]. Here, a basis set extrapolation (as shown above) and a larger supercell are necessary to get closer to the result of 4.7 eV. Please redo the calculation without the flag PERIODIC in the GW section and see that the resulting gap of 11.25 eV is much more off than the gap with correction. +The basis can be found in {{exercises:2017_uzh_cp2k-tutorial:LiH_BASIS_RI.tar ?direct&400 |}}. Then run the calculation as listed below. The computed gap of LiH with the input from below should be 6.05 eV which is still significantly off from the converged result of 4.7 eV from [[doi>10.1103/PhysRevB.95.235123]] [7]. Here, a basis set extrapolation (as shown above) and a larger supercell are necessary to get closer to the result of 4.7 eV. Please redo the calculation without the flag PERIODIC in the GW section and see that the resulting gap of 11.25 eV is much more off than the gap with correction. 
  
 <code - LiH_periodic.inp> <code - LiH_periodic.inp>
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   &DFT   &DFT
     ! retrieve basis set from the CP2K trunk version     ! retrieve basis set from the CP2K trunk version
-    BASIS_SET_FILE_NAME BASIS_def2_QZVP_ALL+    BASIS_SET_FILE_NAME BASIS_def2_QZVP_RI_ALL
     POTENTIAL_FILE_NAME POTENTIAL     POTENTIAL_FILE_NAME POTENTIAL
     &MGRID     &MGRID
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           IM_TIME           IM_TIME
           &IM_TIME           &IM_TIME
 +            ! EPS_FILTER_IM_TIME should be tuned for the specific 
 +            ! application: the computational cost strongly 
 +            ! depends on EPS_FILTER
             EPS_FILTER_IM_TIME 1.0E-12             EPS_FILTER_IM_TIME 1.0E-12
             ! for large systems, increase GROUP_SIZE_3C               ! for large systems, increase GROUP_SIZE_3C  
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             ! to use OMP threads to prevent OOM             ! to use OMP threads to prevent OOM
             GROUP_SIZE_P 1             GROUP_SIZE_P 1
 +            ! for larger systems, MEMORY_CUT must be increased
 +            ! to prevent out of memory (OOM)
 +            MEMORY_CUT  1
             GW             GW
           &END IM_TIME           &END IM_TIME
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