qmmm_example6

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