Rep:Mod:jhl416

Part 1

BH₃

B3LYP/6-31G(d,p)

Summary Table:

         Item               Value     Threshold  Converged?
 Maximum Force            0.000013     0.000450     YES
 RMS     Force            0.000007     0.000300     YES
 Maximum Displacement     0.000053     0.001800     YES
 RMS     Displacement     0.000026     0.001200     YES

Frequency file: BH3_631G_FREQ_JHL416.log

 Low frequencies ---   -7.5477   -1.5512   -0.0054    0.6554    6.9821    7.1523
 Low frequencies --- 1162.9679 1213.1635 1213.1662

Optimised molecule

Vibrational spectrum for BH₃

	Wavenumber (cm-1)	Intensity (arbitrary units)	IR active?	Type
1.	1162	92	Yes	Out-of-plane bend
2.	1213	14	Slightly	Bend
3.	1213	14	Slightly	Bend
4.	2582	0	No	Symmetric stretch
5.	2715	126	Yes	Asymmetric stretch
6.	2715	126	Yes	Asymmetric stretch

Ng611 (talk) 18:21, 30 May 2018 (BST) Good results! You should also include symmetry labels for each of the modes.

IR Spectrum:

Despite having 6 vibrations, there are only 3 vibrational peaks in the IR spectrum. This is due to firstly, the absence of vibration #4 at 2582(cm^-1) as it is an IR inactive symmetric stretch. Secondly, there are 2 sets of degenerate vibrations, which are #2 & #3, and #5 & #6. The degenerate vibrations are observed as one single vibrational peak in the spectrum. Thus, only 3 peaks can be observed in the IR spectrum.

Ng611 (talk) 18:21, 30 May 2018 (BST) Good discussion!

MO diagram of BH₃

The above shows the MO diagram of BH₃ together with the 'real' MOs computed using GaussView. It can be seen that the LCAO MOs highly resembles the computed MOs. This indicates the high accuracy of the qualitative MO theory, which means it can be very useful to predict the shape of orbitals and molecules.

Ng611 (talk) 18:22, 30 May 2018 (BST) Very true. Are there any differences you can see at all?

NH₃

B3LYP/6-31G(d,p)

Summary Table:

         Item               Value     Threshold  Converged?
 Maximum Force            0.000013     0.000450     YES
 RMS     Force            0.000006     0.000300     YES
 Maximum Displacement     0.000039     0.001800     YES
 RMS     Displacement     0.000013     0.001200     YES

Frequency file: NH3_631G_FREQ_JHL416.log

 Low frequencies ---   -8.5646   -8.5588   -0.0047    0.0454    0.1784   26.4183
 Low frequencies --- 1089.7603 1694.1865 1694.1865

Optimised molecule

NH₃BH₃

B3LYP/6-31G(d,p)

Summary Table:

         Item               Value     Threshold  Converged?
 Maximum Force            0.000114     0.000450     YES
 RMS     Force            0.000059     0.000300     YES
 Maximum Displacement     0.000745     0.001800     YES
 RMS     Displacement     0.000345     0.001200     YES

Frequency file: NH3BH3_631G_FREQ_JHL416.log

 Low frequencies ---    0.0013    0.0014    0.0014    3.7980   18.8178   41.9105
 Low frequencies ---  266.4229  632.1415  638.5829

Optimised molecule

Energy determination

E(NH₃)= -56.558 a.u.

E(BH₃)= -26.615 a.u.

E(NH₃BH₃)= -83.225 a.u.

ΔE = E(NH₃BH₃)-[E(NH₃)+E(BH₃)] = -0.052 a.u. = -136.526 kJ/mol

Ng611 (talk) 18:23, 30 May 2018 (BST) You're off by a little bit here (I think it's probably a result of you going to 3 d.p instead of the recommended 5 d.p)

BBr₃

B3LYP/6-31G(d,p)LANL2DZ

Summary Table:

         Item               Value     Threshold  Converged?
 Maximum Force            0.000024     0.000450     YES
 RMS     Force            0.000012     0.000300     YES
 Maximum Displacement     0.000091     0.001800     YES
 RMS     Displacement     0.000040     0.001200     YES

Frequency file: BBr3_GEN_FREQ_JHL416.log ( DOI:10042/202426 )

 Low frequencies ---   -5.9135   -3.4120   -2.3684    0.0002    0.0002    0.0002
 Low frequencies ---  155.8395  155.9338  267.7016

Optimised molecule

Part 2 Mini-project: Main group halides

Ng611 (talk) 18:25, 30 May 2018 (BST) You're missing your point groups here.

Isomer (1) (2 bridging Br ions)

B3LYP/6-31G(d,p)LANL2DZ

Summary Table:

         Item               Value     Threshold  Converged?
 Maximum Force            0.000024     0.000450     YES
 RMS     Force            0.000009     0.000300     YES
 Maximum Displacement     0.000207     0.001800     YES
 RMS     Displacement     0.000098     0.001200     YES

Frequency file: Al2Cl4Br2_ISO1_GEN_FREQ_JHL416_2.log ( DOI:10042/202436 )

Optimised molecule

Isomer (2) (trans terminal Br and bridging Cl ions)

B3LYP/6-31G(d,p)LANL2DZ

Summary Table:

         Item               Value     Threshold  Converged?
 Maximum Force            0.000069     0.000450     YES
 RMS     Force            0.000028     0.000300     YES
 Maximum Displacement     0.001111     0.001800     YES
 RMS     Displacement     0.000486     0.001200     YES

Frequency file: Al2Cl4Br2_ISO2_GEN_FREQ_JHL416_2.log ( DOI:10042/202438 )

 Low frequencies ---   -4.9115   -2.9474   -1.6704   -0.0019   -0.0012   -0.0008
 Low frequencies ---   17.5237   48.9442   72.9542

Optimised molecule

Relative stability

E(isomer 1)= -2352.406 a.u.

E(isomer 2)= -2352.416 a.u.

As isomer 2 lies at a deeper energy than the isomer 1, computed results show that isomer 2 is a more stable isomer. As Al and Cl both lies on the same period on the periodic table, there are better orbital overlap between the bond of Al and Cl than that between Al and Br. Thus, when Cl atoms are used as bridging ions, the overall energy of the molecule is more stable leads to a lower energy.

Ng611 (talk) 18:27, 30 May 2018 (BST) Good! I would actually calculate the energy difference between the molecules to strengthen this section further.

Determination of dissociation energy

AlCl₂Br

B3LYP/6-31G(d,p)LANL2DZ

Summary Table:

         Item               Value     Threshold  Converged?
 Maximum Force            0.000081     0.000450     YES
 RMS     Force            0.000042     0.000300     YES
 Maximum Displacement     0.001588     0.001800     YES
 RMS     Displacement     0.000974     0.001200     YES

Frequency file: AlCl2Br_GEN_FREQ_JHL416.log ( DOI:10042/202440 )

 Low frequencies ---   -0.0055   -0.0052   -0.0050    1.3568    3.6367    4.2604
 Low frequencies ---  120.5042  133.9178  185.8950

Optimised molecule

Calculations of dissociation energy from isomer 2 to 2AlCl₂Br

E(AlCl₂Br) = -1176.190 a.u.

E(Al₂Cl₄Br₂) = -2352.416 a.u.

ΔE = 2 * E(AlCl₂Br)- E(Al₂Cl₄Br₂) = 0.036 a.u. = 94.518 kJ/mol

Ng611 (talk) 18:29, 30 May 2018 (BST) Remember to report your final value to the nearest Kj/mol.

The product is more stable as it is a positive change in energy.

Ng611 (talk) 18:29, 30 May 2018 (BST) What is the product here? Do you mean the dimer? Try to be more specific.

Analysis of 3 molecular orbitals from isomer 2

The following are 3 LACO MO diagrams using the computed results.

Ng611 (talk) 18:31, 30 May 2018 (BST) There's a slight contribution from the two terminal chlorine atoms that should be accounted for. It may be that they're a computational artefact, but you need to mention that you've treated them as such.

Ng611 (talk) 18:31, 30 May 2018 (BST) Good LCAO and Good decomposition

Ng611 (talk) 18:35, 30 May 2018 (BST) Good report. You let yourself down slightly by missing a couple parts out, and with a few accuracy errors when reporting your final results. Otherwise, a good effort. Well done.