! Number of unit cell replications, increase this to create a large polymer.
@SET NREPX 1
@SET NREPY 1

&GLOBAL
  PROJECT 2d_polymer
  RUN_TYPE ENERGY
&END GLOBAL

&FORCE_EVAL
  &DFT
    ! linear scaling SCF
    &LS_SCF
      ! TRS4, does not need an estimate for the chemical potential
      PURIFICATION_METHOD TRS4
      ! threshold used to determine sparsity and thus speed and accuracy
      EPS_FILTER 1E-5  
      ! convergence for the SCF
      EPS_SCF    1E-15
      MAX_SCF 30
      ! 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

    &QS
      LS_SCF  ! Turns on linear scaling DFT. Comment this line to run with standard SCF.

      ! =============================================================================================
      ! === Description of Hamiltonian (Density Functional Tight Binding + Smooth Particle Meshed Ewald) ===
      METHOD DFTB
      &DFTB
        HB_SR_GAMMA 
        SELF_CONSISTENT    T
        DO_EWALD           T
        DISPERSION         T
        &PARAMETER
          PARAM_FILE_PATH  ./dftb_params/scc
          PARAM_FILE_NAME  scc_parameter
          UFF_FORCE_FIELD  uff_table
        &END PARAMETER
      &END DFTB
    &END QS

    &POISSON
      &EWALD
       EWALD_TYPE SPME
       ! scale the number of points with the system size, roughly 1pt/A.
       GMAX 40*${NREPX} 40*${NREPY} 40
       O_SPLINE 5
      &END EWALD
    &END POISSON
   ! ==============================End of Hamiltonian Description ================================
   ! =============================================================================================
  &END DFT

  
  &SUBSYS
    &CELL
      ! a 2D system, z-direction is non-periodic
      ABC 23.577999 40.8383 30
      MULTIPLE_UNIT_CELL ${NREPX} ${NREPY} 1
    &END CELL
    &TOPOLOGY
      MULTIPLE_UNIT_CELL ${NREPX} ${NREPY} 1
    &END
    &COORD
@INCLUDE '2d_polymer.coord' 
    &END COORD
  &END SUBSYS
&END FORCE_EVAL