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exercises:2015_ethz_mmm:ls_scf

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exercises:2015_ethz_mmm:ls_scf [2015/02/06 17:49] – external edit 127.0.0.1exercises:2015_ethz_mmm:ls_scf [2020/08/21 10:15] (current) – external edit 127.0.0.1
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 ====== Linear Scaling Self Consistent Field Methods ====== ====== Linear Scaling Self Consistent Field Methods ======
  
-In this exercise we will compare linear scaling with normal SCF methods. We will run simulations on a 2D polymer system containing up to 2400 atoms. The 2D polymer system is described in more detail in this recent publication [[doi>10.1002/adma.201304705]]. To make this exercise computationally feasible, will us the efficient Density Functional based Tight Binding (DFTB) method. It requires only a minima basis, but delivers nevertheless reasonable results due to an empirical correction term called //repulsion potential//.+In this exercise we will compare linear scaling SCF [[doi>10.1021/ct200897x]] with normal SCF methods. We will run simulations on a 2D polymer system containing up to 2400 atoms. The 2D polymer system is described in more detail in this recent publication [[doi>10.1002/adma.201304705]]. To make this exercise computationally feasible, will us the efficient Density Functional based Tight Binding (DFTB) method [[doi>10.1103/PhysRevB.58.7260]]. It requires only a minima basis, but delivers nevertheless reasonable results due to an empirical correction term called //repulsion potential//.
  
 <note tip> <note tip>
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 ===== Input File ===== ===== Input File =====
 <code - 2d_polymer.inp> <code - 2d_polymer.inp>
 +! Number of unit cell replications, increase this to create a large polymer.
 +@SET NREPX 1
 +@SET NREPY 1
 +
 &GLOBAL &GLOBAL
   PROJECT 2d_polymer   PROJECT 2d_polymer
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 &FORCE_EVAL &FORCE_EVAL
   &DFT   &DFT
 +    ! linear scaling SCF
     &LS_SCF     &LS_SCF
-      EPS_FILTER 1E-5  ! threshold used to determine sparsity +      ! TRS4, does not need an estimate for the chemical potential 
-      MU         -0.15 ! chemical potential, an energy from within in the HOMO-LUMO gap+      PURIFICATION_METHOD TRS4 
 +      ! threshold used to determine sparsity and thus speed and accuracy 
 +      EPS_FILTER 1E-5   
 +      ! convergence for the SCF 
 +      EPS_SCF    1E-5 
 +      ! chemical potential, an energy from within in the HOMO-LUMO gap 
 +      MU         -0.15  
 +      S_PRECONDITIONER ATOMIC 
 +    &END 
 + 
 +    ! traditional SCF, diagonalization by default 
 +    &SCF
     &END     &END
  
     &QS     &QS
-      LS_SCF  ! Turns on linear scaling DFT. Comment this line to run with normal SCF.+      LS_SCF  ! Turns on linear scaling DFT. Comment this line to run with standard SCF.
  
-! ============================================================================================= +      ! ============================================================================================= 
-! === Description of Hamiltonian (Density Functional Tight Binding + Particle Meshed Ewald) ===+      ! === Description of Hamiltonian (Density Functional Tight Binding + Smooth Particle Meshed Ewald) ===
       METHOD DFTB       METHOD DFTB
       &DFTB       &DFTB
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         DISPERSION         T         DISPERSION         T
         &PARAMETER         &PARAMETER
-          PARAM_FILE_PATH  ./dftb_params/scc+          PARAM_FILE_PATH  ./DFTB/scc
           PARAM_FILE_NAME  scc_parameter           PARAM_FILE_NAME  scc_parameter
           UFF_FORCE_FIELD  uff_table           UFF_FORCE_FIELD  uff_table
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       &END DFTB       &END DFTB
     &END QS     &END QS
 +
     &POISSON     &POISSON
       &EWALD       &EWALD
        EWALD_TYPE SPME        EWALD_TYPE SPME
-       GMAX 160+       ! scale the number of points with the system size, roughly 1pt/A. 
 +       GMAX 40*${NREPX} 40*${NREPY} 40
        O_SPLINE 5        O_SPLINE 5
       &END EWALD       &END EWALD
     &END POISSON     &END POISSON
-! ==============================End of Hamiltonian Description ================================ +   ! ==============================End of Hamiltonian Description ================================ 
-! =============================================================================================+   ! =============================================================================================
   &END DFT   &END DFT
  
-! Number of unit cell replications, increase this to create a large polymer. 
-@SET NREP 1 
      
   &SUBSYS   &SUBSYS
     &CELL     &CELL
 +      ! a 2D system, z-direction is non-periodic
       ABC 23.577999 40.8383 30       ABC 23.577999 40.8383 30
-      MULTIPLE_UNIT_CELL 1 ${NREP} 1+      MULTIPLE_UNIT_CELL ${NREPX} ${NREPY} 1
     &END CELL     &END CELL
     &TOPOLOGY     &TOPOLOGY
-      MULTIPLE_UNIT_CELL 1 ${NREP} 1+      MULTIPLE_UNIT_CELL ${NREPX} ${NREPY} 1
     &END     &END
     &COORD     &COORD
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   &END SUBSYS   &END SUBSYS
 &END FORCE_EVAL &END FORCE_EVAL
 +
 </code> </code>
  
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