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Administrator<br />

• Overall errors in ∆H f are reduced by about<br />

40% relative to AM1.<br />

• Little information exists regarding the<br />

limitations of PM3. This should be corrected<br />

naturally as results of PM3 calculations are<br />

reported.<br />

• The barrier to rotation in formamide is<br />

practically non-existent. In part, this can be<br />

corrected by the use of the MMOK option.<br />

The MMOK option is used by default in CS<br />

MOPAC. For more information about<br />

MMOK see the online MOPAC Manual.<br />

MNDO-d Applicability and Limitations<br />

MNDO-d (Modified Neglect of Differential<br />

Overlap with d-Orbitals) may be applied to the<br />

elements shaded in the table below:<br />

• GREENF (Green’s Function)<br />

• TOM (Miertus-Scirocco-Tomasi<br />

self-consistent reaction field model for<br />

solvation)<br />

Using Keywords<br />

Selecting parameters for a MOPAC approximation<br />

automatically inserts keywords in a window on the<br />

General tab of the MOPAC Interface. You can<br />

edit these keywords or use additional keywords to<br />

perform other calculations or save information to<br />

the *.out file.<br />

CAUTION<br />

Use the automatic keywords unless you are an advanced<br />

MOPAC user. Changing the keywords may give<br />

unreliable results.<br />

For a complete list of keywords see the MOPAC<br />

online manual.<br />

Automatic Keywords<br />

The following contains keywords automatically<br />

sent to MOPAC and some additional keywords you<br />

can use to affect convergence.<br />

MNDO-d is a reformulation of MNDO with an<br />

extended basis set to include d-orbitals. This<br />

method may be applied to the elements shaded in<br />

the table below. Results obtained from MNDO-d<br />

are generally superior to those obtained from<br />

MNDO. The MNDO method should be used<br />

where it is necessary to compare or repeat<br />

calculations previously performed using MNDO.<br />

The following types of calculations, as indicated by<br />

MOPAC keywords, are incompatible with<br />

MNDO-d:<br />

• COSMO (Conductor-like Screening Model)<br />

solvation<br />

• POLAR (polarizability calculation)<br />

Keyword<br />

EF<br />

BFGS<br />

GEO-OK<br />

Description<br />

Automatically sent to MOPAC to<br />

specify the use of the Eigenvector<br />

Following (EF) minimizer.<br />

Prevents the automatic insertion<br />

of EF and restores the BFGS<br />

minimizer.<br />

Automatically sent to MOPAC to<br />

override checking of the Z-matrix.<br />

166•MOPAC <strong>Com</strong>putations<br />

<strong>CambridgeSoft</strong><br />

Using Keywords

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