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 Data\Parameter Set". When MOPAC is used with a GUI, e.g. Chem-3D, always use the full path name for the external file, i.e. use, e.g., EXTERNAL="E:\Test Data\Parameter Set" and not, e.g., EXTERNAL="Parameter Set".
<filename> contains a series of parameter definitions in the format:
<Parameter> <Element> <Value of parameter>
where the possible parameters are USS, UPP, UDD, ZS, ZP, ZD, BETAS, BETAP, BETAD, GSS, GSP, GPP, GP2, HSP,
F0SD, G2SD, ALP, FNnm, n=1,2, or 3, and m=1 to 10, and the elements are defined by their chemical symbols, such as Si or SI.
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|
Line 1: USS Si -34.08201495 Line 2: UPP Si -28.03211675 Line 3: BETAS Si -5.01104521 Line 4: BETAP Si -2.23153969 Line 5: ZS Si 1.28184511 Line 6: ZP Si 1.84073175 Line 7: ALP Si 2.18688712 Line 8: GSS Si 9.82 Line 9: GPP Si 7.31 Line 10: GSP Si 8.36 Line 11: GP2 Si 6.54 Line 12: HSP Si 1.32 Line 13: BETAD TC -5.72433498 Line 14: F0SD TC 5.43488602 Line 15: G2SD TC 1.10687502 Line 16: XFAC_Ag I 2.0 Line 17: ALPB_C Rb 2.0 |
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.