MOLPRO

53 QM/MM INTERFACES 373
53 QM/MM INTERFACES
The MOLPRO program package can be used in combination with other software to perform
hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) calculations. Through the use
of point charges, electrostatic embedding can be used for both energy and gradient runs. In
particular, lattices of point charges can be included in an external file, gradients with respect to
charge positions can be computed, as described in section 10.5. Gradients with respect to QM
nuclear positions can be computed (and include the effect of the MM charges) as usual using
the FORCE command (section 41).
Although MOLPRO itself does not offer any interface to force field programs, the coupling is
supplied by other commercial and non-commercial software. The following is a list of QM/MM
software which allow the use of MOLPRO.
53.1 Chemshell
The Chemshell computational chemistry environment (http://www.chemshell.org) offers an interface
to many well known force field software (CHARMM, GROMOS, GULP,...). The program
sports several geometry optimization algorithms; a molecular dynamics driver for NV E,
NV T and NPT ensembles; Monte Carlo; and many other utilities.
The Chemshell Manual can be found at the following website:
http://www.cse.scitech.ac.uk/ccg/software/chemshell/manual/
Instructions on the use of Molpro are available therein. Also concerning the Chemshell environment,
a free Graphical User Interface (GUI) has been released. The CCP1GUI facilitates the
input for hybrid calculations, allows visualisation of molecular structures and includes molecule
editing tools:
http://www.cse.scitech.ac.uk/ccg/software/ccp1gui/
54 THE TDHF AND TDKS PROGRAMS
Real-time electronic dynamics using time-dependent Hartree-Fock and time-dependent Kohn-
Sham theories can be performed using the commands TDHF and TDKS respectively, which have
to be preceded by a HF and KS command. Unrestriced versions are available through TDUHF
and TDUKS and should be preceded by UHF and UKS runs respectively. All methods require
symmetry to be switched off. For details on the theory and methods see H. Eshuis, G. G.
Balint-Kurti and F. R. Manby, J. Chem. Phys. 128, 114113 (2008), and references therein. The
commands take several options:
command,t=,dt=,ns=,ng=,grsize=,print=;
PULSE,options
The total propagation time (in au) is set by t; dt sets the timestep and ns the number of steps,
where two of the three have to be provided. ng sets the number of grid points in one dimension
(default = 0) and grsize the grid size in bohr (default = 10 bohr). Setting ng > 2 switches
on the calculation of quantum currents (see below). The option print determines the level of