# Qmmm sp

### From NWChem

# QM/MM Single Point Energy/Gradient Calculations

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

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