Qmmm sp energy

From NWChem

QMMM Single Point Calculations: Ground State Energy and Gradient | Excited State Energy| Properties | ESP

The task directive for QM/MM single point energy and gradient calculations is given by

task qmmm <qmtheory> energy

or

task qmmm <qmtheory> gradient [numerical]

where qmtheory refers to the level of QM theory (e.g. dft, tce, mp2, ...).

The ground state QM/MM energy calculations should be possible with all QM descriptions available in NWChem, however most of testing was performed using core QM methods (scf,dft,mp2,tce). The ground state QM/MM gradient calculations can be performed analytically with scf,dft,mp2 levels of theory and numerically for all the others.

The relevant settings for QM/MM interface block for energy and gradient calculations include

• bqzone
• mm_charges
• link_atoms
• link_ecp.

The example below illustrates single point energy calculation at DFT/B3LYP level for ethanol molecule embedded into 20 angstrom box of SPCE/E water molecules.

  start etl
  permanent_dir ./perm
  scratch_dir ./data
  prepare
  source etl0.pdb
  new_top new_seq
  new_rst
  modify atom 1:_C1  quantum
  modify atom 1:2H1  quantum
  modify atom 1:3H1  quantum
  modify atom 1:4H1  quantum
  center
  orient
  solvate box 3.0
  update lists
  ignore
  write etl_ref.rst
  write etl_ref.pdb
  end
  task prepare
  md
  system etl_ref
  end
  basis
  * library "6-31G"
  end
  dft
  xc b3lyp
  end
  qmmm
    link_atoms hydrogen
  end
  task qmmm dft energy