Rep:Mod:comp chem lab testpage5

Demo page for the lab

NH₃

B3LYP/6-31G(d,p)

          Item               Value     Threshold  Converged?
 Maximum Force            0.000056     0.000450     YES
 RMS     Force            0.000030     0.000300     YES
 Maximum Displacement     0.000136     0.001800     YES
 RMS     Displacement     0.000068     0.001200     YES

Frequency file: nh3_frequency.log

 Low frequencies ---  -29.1845  -27.0206  -27.0196    0.0008    0.0022    0.0076
 Low frequencies ---  763.1907 1745.2285 1745.2285

optimised BH3 molecule

Don't forget that my file is for NH₃ and not BH₃!

Also note that my lowest frequency is outside of the ±15 cm^-1 range!

If this happens to your BH₃ molecule, then something is wrong and ask a demonstrator for help!!

In this case, for NH₃, the formally zero frequencies are well separated from the lowest energy positive frequency at 1088cm^-1 and the large formally zero frequencies are due to the low level of the basis set and relatively relaxed convergence and integration criteria. This can happen for small molecules.

Vibrational spectrum for NH₃

wavenumber (cm-1	Intensity (arbitrary units)	symmetry	IR active?	type
763	260	A1	yes	out-of-plane bend
1745	14	E	very slight	bend
1745	14	E	very slight	bend
3390	1	A1	no	symmetric stretch
3543	1	E	no	asymmetric stretch
3543	1	E	no	asymmetric stretch

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This is where you add your explanation of why there are fewer vibrational peaks than there are vibrations.(In your wiki explain why are there less than six peaks in the spectrum, when there are obviously six vibrations.)

PP and basis sets

Frequency file: Media:File:6-31G(d,p)LANL2DZ NI3.txt

         Item               Value     Threshold  Converged?
 Maximum Force            0.000067     0.000450     YES
 RMS     Force            0.000044     0.000300     YES
 Maximum Displacement     0.000492     0.001800     YES
 RMS     Displacement     0.000333     0.001200     YES

optimised NI3

The optimized distance is 2.1836

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