Rep:Mod:vsvp2109

3rd Year Computational Lab - Module 2

Introduction

Intro goes here... Gaussview 5 and Gaussian were used

Optimisation of a molecule

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BH₃ - B3LYP, 3-21G optimisation

Results from log file and Gaussview summary provided below:

Figure 1 - BH₃ Optimisation Summary

         Item               Value     Threshold  Converged?
 Maximum Force            0.000413     0.000450     YES
 RMS     Force            0.000271     0.000300     YES
 Maximum Displacement     0.001610     0.001800     YES
 RMS     Displacement     0.001054     0.001200     YES

1)

Preview of optimised molecule

BH₃ - B3LYP, 6-31G d,p optimisation

Results from log fileand Gaussview summary provided below:

Figure 4 - BH₃ Optimisation Summary 6-31g d,p

         Item               Value     Threshold  Converged?
 Maximum Force            0.000005     0.000450     YES
 RMS     Force            0.000003     0.000300     YES
 Maximum Displacement     0.000020     0.001800     YES
 RMS     Displacement     0.000012     0.001200     YES

Preview of optimised molecule

Total energies of BH₃ optimisations

Total energy for your 3-21G optimised structure = -26.46226338a.u.
Total energy for your 6-31G(d,p) optimised structure = -26.61532374a.u.

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TlBr₃ - optimisations using pseudo-potentials (LanL2DZ)

Results from log file and Gaussview summary provided below:

Figure 1 - TlBr₃ Optimisation Summary

        Item               Value     Threshold  Converged?
Maximum Force            0.000002     0.000450     YES
RMS     Force            0.000001     0.000300     YES
Maximum Displacement     0.000022     0.001800     YES
RMS     Displacement     0.000014     0.001200     YES

Optimised molecule of TlBr₃
2) literature values are: 232Å and 120°

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BBr₃ - optimisation using a mixture of basis sets and pseudo potentials

Results from log fileand Gaussview summary provided below:

Figure 1 - BBr₃ Optimisation Summary

         Item               Value     Threshold  Converged?
 Maximum Force            0.000008     0.000450     YES
 RMS     Force            0.000005     0.000300     YES
 Maximum Displacement     0.000037     0.001800     YES
 RMS     Displacement     0.000024     0.001200     YES

Preview of optimised molecule

3)

Comparison of bond distances

The bond lengths of the 3 molecules investigated are summarised in the table below:

Molecule	bond lengths, Å
BH3	1.1933333
BBr3	1.9333333
TlBr3	2.655555

4), 5)

Frequency analysis

BH₃ vibrational analysis

Gaussview summary provided below:

Figure 6 - BH₃ Frequency Analysis Summary

Results from frequency analysis

         Item               Value     Threshold  Converged?
 Maximum Force            0.000004     0.000450     YES
 RMS     Force            0.000002     0.000300     YES
 Maximum Displacement     0.000022     0.001800     YES
 RMS     Displacement     0.000010     0.001200     YES

 Low frequencies ---   -3.4213   -0.0026   -0.0004    0.0015    3.9367    3.9367
 Low frequencies ---   46.4289   46.4292   52.1449

Normal modes of vibration (as predicted) are presented in the table below:

Number	Vibrational Mode	Frequency/ cm-1	Intensity/ cm-1	Symmetry Point group	Brief description
1		1162.98	92.5514	A2'
2		1213.17	14.0573	E'
3		1213.24	14.0608	E'	You just can't explain it
4		2582.26	0	A1'	Symmetric stretch of hydrogen atoms (in the plane of the molecule); boron in fixed position
5		2715.42	126.3279	E'
6		2715.44	126.3242	E'

IR spectrum presented below:

Figure 99 - BH₃ Infrared Spectrum

TlBr₃ vibrational analysis

Gaussview summary provided below:

Figure 6 - TlBr₃ Frequency Analysis Summary

         Item               Value     Threshold  Converged?
 Maximum Force            0.000002     0.000450     YES
 RMS     Force            0.000001     0.000300     YES
 Maximum Displacement     0.000022     0.001800     YES
 RMS     Displacement     0.000011     0.001200     YES

Completed frequency analysis of TlBr₃

Number	Vibrational Mode	Frequency/ cm-1	Intensity/ cm-1	Symmetry Point group	Brief description
1		46	3.7	E'
2		46	3.7	E'
3		52	5.8	A2'
4		165	0	A1'
5		211	25	E'
6		211	25	E'

IR spectrum presented below:

Figure 99 - TlBr₃ Infrared Spectrum

NH3

Figure 95 - NH₃ Summary

         Item               Value     Threshold  Converged?
 Maximum Force            0.000024     0.000450     YES
 RMS     Force            0.000012     0.000300     YES
 Maximum Displacement     0.000079     0.001800     YES
 RMS     Displacement     0.000053     0.001200     YES
 Predicted change in Energy=-1.629659D-09
 Optimization completed.
    -- Stationary point found.