Chem3D 8.0 Manual - CambridgeSoft

Dipole MomentThe dipole moment is the first derivative of theenergy with respect to an applied electric field. Itmeasures the asymmetry in the molecular chargedistribution and is reported as a vector in threedimensions.The dipole value will differ when you chooseMulliken Charges, Wang-Ford Charges orElectrostatic Potential, as a different density matrixis used in each computation.NOTE: For more information see the MOPACmanual, page 119.The following table contains the keywordsautomatically sent to MOPAC.KeywordGEO-OKMMOKDescriptionThe Dipole Moment ofFormaldehydeTo calculate the dipole moment of formaldehyde:1. From the File menu, choose New Model.2. Click the Text Building tool.3. Click in the model window.A text box appears.Automatically sent to MOPACto override checking of theZ-matrix.Automatically sent to MOPACto specify Molecular Mechanicscorrection for amide bonds. Usethe additional keyword NOMMto turn this keyword off.4. Type “H2CO” and press Enter.A model of formaldehyde appears.5. From the MOPAC menu, choose MinimizeEnergy.6. On the Theory tab, choose AM1.7. On the Properties tab, select Dipole.8. Click Run.The results shown in the Messages window indicatethe electron distribution is skewed in the direction ofthe oxygen atom.Dipole(vectorDebye)If you rotate your model, the X,Y, and Z componentsof the dipole differ. However, the total dipole doesnot. In this example, the model is oriented so that thesignificant component of the dipole lies along theX-axis.ChargesX Y Z Total- 0.000 - 2.3172.3170.000The property, Charges, determines the atomiccharges using a variety of techniques discussed inthe following sections. In this example the chargesare the electrostatic potential derived charges fromWang-Ford, because Wang-Ford charges give usefulinformation about chemical stability (reactivity).Chem3D 8 Chapter 11: MOPAC Computations • 163Compute Properties