Molecularmechanics1.Ball and spring description of molecules;2.Betterrepresentationofeguilibriumgeometries than plastic models;3.Ableto computerelative strainenergies;4.Cheap to compute;5.Lots ofempiricalparametersthathavetobecarefullytested and calibrated;water6.Limited to equilibrium geometries;ContinuumsolventmodelHydrophobic effect is roughlyproportionaltosurfacearea7.Does nottake electronic interactions intoaccount;8.No information on reactivity;W9.Cannot readily handle reactions involvingtorsion anglethemakingandbreaking ofbonds.LennardJonesDistancebond length or 3-atom angle17
Molecular mechanics 1. Ball and spring description of molecules; 2. Better representation of equilibrium geometries than plastic models; 3. Able to compute relative strain energies; 4. Cheap to compute; 5. Lots of empirical parameters that have to be carefully tested and calibrated; 6. Limited to equilibrium geometries; 7. Does not take electronic interactions into account; 8. No information on reactivity; 9. Cannot readily handle reactions involving the making and breaking of bonds 17
Semi-empiricalmolecularorbitalmethods1. Approximate description of valence electrons;2. Obtained by solving a simplified form of theSchrodinger equation;3.Many integrals approximated using empiricalexpressions with various parameters;4. Semi-quantitative description of electronicdistribution, molecular structure, properties andrelative energies;5. Cheaper than ab initio electronic structure methodsbut not as accurate18
Semi-empirical molecular orbital methods 1. Approximate description of valence electrons; 2. Obtained by solving a simplified form of the Schrödinger equation; 3. Many integrals approximated using empirical expressions with various parameters; 4. Semi-quantitative description of electronic distribution, molecular structure, properties and relative energies; 5. Cheaper than ab initio electronic structure methods, but not as accurate 18