Computational Chemistry

2. Theenergyof a molecular species relative to the energies of other species
   on a potential energy surface is fundamental to a knowledge of its kinetic
   and thermodynamic behaviour, and this can be important in attempts to
   synthesize it.


3. Thevibrational frequenciesof a molecule provide information about the elec-
   tronic nature of its bonds, and prediction of the spectra represented by these
   frequencies may be useful to experimentalists.
   A fourth important characteristic of a molecule is thedistribution of electron
   densityin it. Calculation of the electron density distribution enables one to predict
   the dipole moment, the charge distribution, the bond orders, and the shapes of
   various molecular orbitals.

80

60

40

20

0

IR_INTENS

0

5.3

1.1e+002

1.6e+002

4000

4000

3000

3500 3000

2000

FREQ_VAL

FREQ_VAL

2500 2000

1000

1500 1000 500

Dichloromethane

Experimental

HF / 6-31G*

1451

1378

817

843

1261

757

1276

IR_INTENS

0

4.3

87

1.3e+002

4000 3500 3000 2500 2000 1500 1000 500

MP2 / 6-31G*

Fig. 5.35 Experimental (gas phase), HF/6–31G and MP2(fc)/6–31G calculated IR spectra of
dichloromethane

5.5 Applications of the Ab initio Method 339