Note
This website is presently under development. The primary website for MOPAC is still http://openmopac.net until the majority of its contents have been migrated here.
EXTERNAL¶
EXTERNAL=name
Atom parameters
Normally, all semiempirical parameters are taken from the module files
within MOPAC. When the supplied parameters are not suitable, as in an
element recently parameterized, and the parameters have not yet
installed in the user’s copy of MOPAC, then the new parameters can be
inserted at run time by use of EXTERNAL=<filename>, where
<filename> is the name of the file which contains the new
parameters. If the file-name contains spaces, then enclose the filename
in quotation marks, e.g. ``EXTERNAL=”E:Test DataParameter Set”. ``
<filename>contains a series of parameter definitions in the format:````
<Parameter> <Element> <Value of parameter>
where the possible parameters
areUSS, UPP, UDD, ZS, ZP, ZD, BETAS, BETAP, BETAD, GSS, GSP, GPP, GP2, HSP, F0SD, G2SD, ALP, XFAC_xx, ALPB_xx, FNnm,n=1,2,
or 3, andm=1 to 10, and the elements are defined by their
chemical symbols, such as Si or SI. So FN11 is the first “a” parameter
of the core-core term, FN12 is the second “a” parameter (if it exists),
FN21 is the first “b” parameter of the core-core term, and FN31 is the
first “c” parameter of the core-core term.
When new parameters for elements are published, they can be typed in as shown. This file is ended by a blank line, the word END or nothing i.e., no end-of-file delimiter. An example of a parameter data file is given in the Figure:
Figure: Use of EXTERNAL=name
USS Si -34.08201495
UPP Si -28.03211675
UDD Si -6.0
BETAS Si -5.01104521
BETAP Si -2.23153969
Betad Si -1.0
ZS Si 1.28184511
ZP Si 1.84073175
ALP Si 2.18688712
GSS Si 9.82
GPP Si 7.31
GSP Si 8.36
GP2 Si 6.54
HSP Si 1.32
BETAD TC -5.72433498
F0SD TC 5.43488602
G2SD TC 1.10687502
XFAC_Ag I 2.0
ALPB_C Rb 2.0
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INDO/S parameters¶
Since the parameter structure of INDO is different from NDDO methods, the allowed parameter names are also different. The allowed values for INDO are BETAS, BETAP, BETAD, NORBS, ZCORE, ZSP, ZD1, ZD2, ZWT1, ZWT2, and FGi (i = 1-24). Note that in INDO many parameters for s and p orbitals should be identical, so BETAS should be set to equal BETAP. Both s and p orbital exponents are set up using ZSP.
Derived parameters do not need to be entered; they will be calculated from the optimized parameters. All “constants” such as the experimental heat of atomization are already inserted for all elements.
If a parameter is not set, e.g. UPP for hydrogen, do not attempt to define the parameter as zero. If a parameter that has not been defined is given a defined value of zero, then it will become defined, and have the value zero. From that point on, it would be recognized as a defined parameter, usually with disastrous results. So do not use lines such as:
UPP H 0.0
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Derived parameters do not need to be entered; they will be calculated from the optimized parameters. All “constants” such as the experimental heat of atomization are already inserted for all elements.
Global parameters¶
Most users should not change the values of global parameters; because of this, definitions of global parameters are not provided. Users who need to edit global parameters would normally have access to the source code of MOPAC, and would be able to read and edit the parameters.
Values of global parameters are set and re-set using EXTERNAL lines of the type:
PAR1 1.234
PAR6 2.345
PAR23 3.456