The MNDO Interface

Introduction

The MNDO interface offers the ability to perform semi-empirical energy and force calculations using the MNDO package, which must be built on the system. As for the other energy and gradient routines, this is accomplished by the implementation of a family of routines, including mndo.init, mndo.energy, and mndo.gradient (see description of the general energy/gradient interface for more details).

Control Arguments

The MNDO interface follows the conventions of the general energy/gradient interface and as such the component functions take coords=, energy=, gradient= arguments. Since these are usually provided by driver modules they are not documented here. The MNDO interface complies with the generic quantum interface, see these sections, and accepts the following arguments:

Argument	Argument type	Mandatory	Default	To specify
jobname=	string	no	mndo	name to use as root for file names
listing=	string	no	mndo.out	where to output the job listing (includes option to select stdout)
unique_listing=	boolean	no	no	whether to save each output to a separate file
hamiltonian=	string	no	mndo	choice of QM hamiltonian, mndo, am1, om1, scc (which is SCC-DFTB) etc. Not all hamiltonians are supported by all versions of mndo.
charge=	integer	no	0	Molecular Charge
mult=	integer	no	1	Spin Multiplicity
scftype=	keyword	rhf	1	SCF type
accuracy=	keyword	no	medium	General specification on accuracy of calculation
maxcyc=	integer	no	100	number of SCF cycles permitted

The interface accepts (but ignores) the basis=, basispec=, symmetry= and direct= keywords for compatibility with other quantum mechanical interfaces.

Argument	Argument type	Mandatory	Default	To specify
executable	string	yes	mndo	executable name
verbose	boolean	no	no	controls amount of listing sent to stdout
debug	boolean	no	no	debugging output
restart	Boolean	no	see note 1	restart from a saved SCF guess

1. A restarted calculation usually requires the saved density matrix from the MNDO output file fort.11. In the special case of SCC-DFTB, initial guess charges from the file CHR.dat are used. See the MNDO manual for more details (keyword ktrial).

MNDO Specific Options

The following parameters control MNDO-specific keywords and settings. optstr is used to add arbritrary elements to the MNDO control strings, the other options change the corresponding MNDO control variables. link_atom_indices and link_atom_option are used to access the QM/MM coupling options of MNDO and will usually be provided automatically by the hybrid module.

Argument	Argument type	Mandatory	Default	To specify
optstr	Tcl List	no	" "	list for additional MNDO keywords
link_atom_indices	Tcl List	no	{ }	List of atoms to be treated as Link atoms, usually provided automatically by the hybrid module
link_atom_option	string	no	No special treatment	Treatment for link atoms, (ACA, L1, L2, or shift) usually provided automatically by the hybrid module
binary	Boolean	no	false	Sets data exchange between MNDO and ChemShell via unformatted (binary) files. This minimises loss of accuracy.
iop	integer	no	See Note 1	choice of QM hamiltonian, see MNDO manual
nprint	integer	no	2	Printing flag for SCF, see MNDO manual
iscf	integer	no	6	SCF convergence criterion for the electronic energy, see MNDO manual
iplscf	integer	no	6	SCF convergence criterion for the diagonal of the density matrix, see MNDO manual
iprec	integer	no	1	Option to increase the precision of the convergence criteria for geometry optimisations, see MNDO manual
idiis	integer	no	0	DIIS extrapolation procedure for SCF, see MNDO manual
mmpot	integer	no	0	Definition of the electrostatic potential and the electric field (by implication), see MNDO manual

GUGA ci specific settings

Options specific for microiterative QM/MM optimisation

Notes

1. By default the Hamiltonian is controlled by the hamiltonian= argument.
2. The default is chosen based on other GUGA settings provided.

GUGA CI Examples

# ciorbs = { ... HOMO-1 HOMO LUMO LUMO+1 ... } 

# ciref = { { 2 2 0 0 } { 2 1 1 0 } ... { } }