Qmmm example6

From NWChem

The example below illustrates QM/MM calculation of ElectroStatic Potential (ESP) charges at DFT/B3LYP level of theory for quantum water molecule embedded into 20 angstrom box of classical SPCE/E water molecules.

The preparation stage that involves definition of the QM region and solvation is performed as part of the calculation. Note that water fragment file wtr.frg is required in this calculation. Prepare run will generate restart file (wtr_ref.rst) and topology file (wtr.top).

In the QM/MM interface block the use of bq_zone value of 3.0 Angstrom is specified.

Important: ESP module relies on the availability of movecs (wavefunction) file. In this example, movecs file was generated by performing energy calculation.

  start wtr
  permanent_dir ./perm
  scratch_dir ./data
  prepare
  source wtr0.pdb
  new_top new_seq
  new_rst
  modify segment 1  quantum
  center
  orient
  solvate box 3.0
  update lists
  ignore
  write wtr_ref.rst
  write wtr_ref.pdb
  end
  task prepare
  md
  system wtr_ref
  end
  basis
  * library "6-31G"
  end
  dft
  xc b3lyp
  end
  qmmm
  bq_zone 3.0
  end
  task qmmm dft energy
  task qmmm esp