林奕諄-第七週作業
1.Please use ChatGPT to explore a thematic series of questions within the scope of computational chemistry and follow up with further inquiries about any unfamiliar terms ( except homework )
2.Calculate the structures and atomization energies (AE) of XHn (X = H~Ne) by using B3LYP、MP2 theoretical methods with 6-31+G(d,p)、aug-cc-pVTZ then compare with the experimental values
The tables below are optimized geometry structures.
| LiH | BeH2 | BH3 | CH4 | NH3 | H2O | HF | |
| B3LYP/6-31+G(d,p) | 1.614 | 1.331 | 1.193 | 1.093 | 1.016 | 0.965 | 0.928 |
| B3LYP/aug-cc-pVTZ | 1.590 | 1.325 | 1.188 | 1.088 | 1.013 | 0.962 | 0.924 |
| MP2/6-31+G(d,p) | 1.623 | 1.328 | 1.186 | 1.087 | 1.012 | 0.963 | 0.926 |
| MP2/aug-cc-pVTZ | 1.605 | 1.330 | 1.187 | 1.086 | 1.012 | 0.963 | 0.922 |
| Experimental values | 1.595 | 1.326 | 1.190 | 1.087 | 1.012 | 0.958 | 0.917 |
The calculations are similar. MP2/aug-cc-pVTZ gets best predictions.
| BeH2 | BH3 | CH4 | NH3 | H2O | |
| B3LYP/6-31+G(d,p) | 180.0 | 120.0 | 109.5 | 108.1 | 105.8 |
| B3LYP/aug-cc-pVTZ | 180.0 | 120.0 | 109.5 | 107.2 | 105.1 |
| MP2/6-31+G(d,p) | 180.0 | 120.0 | 109.5 | 108.1 | 105.4 |
| MP2/aug-cc-pVTZ | 180.0 | 120.0 | 109.5 | 106.8 | 104.1 |
| Experimental values | 180.0 | 120.0 | 109.5 | 106.7 | 104.5 |
The calculations are similar.
The atomization energy ΔEa is the extra energy needed to break up a molecule into separate atoms.
| LiH | BeH2 | BH3 | CH4 | NH3 | H2O | HF | |
| B3LYP/6-31+G(d,p) | 57.0 | 153.7 | 286.7 | 422.8 | 300.1 | 229.5 | 138.2 |
| B3LYP/aug-cc-pVTZ | 58.4 | 150.7 | 184.7 | 420.6 | 300.6 | 230.5 | 138.8 |
| MP2/6-31+G(d,p) | 45.1 | 138.7 | 269.4 | 399.3 | 274.8 | 220.4 | 137.0 |
| MP2/aug-cc-pVTZ | 51.8 | 146.0 | 275.4 | 411.3 | 290.1 | 232.1 | 143.3 |
| Experimental values | 55.7 | 149.3 | 266.8 | 392.4 | 276.7 | 219.4 | 135.4 |
Source : Computational Chemistry Comparison and Benchmark DataBase
Figure 1 Atomization energy ( Experimental values )
| LiH | BeH2 | BH3 | CH4 | NH3 | H2O | HF | |
| B3LYP/6-31+G(d,p) | 1.3 | 4.4 | 19.9 | 30.4 | 23.4 | 10.1 | 2.8 |
| B3LYP/aug-cc-pVTZ | 2.7 | 1.4 | 17.9 | 28.2 | 23.9 | 11.1 | 3.4 |
| MP2/6-31+G(d,p) | -10.6 | -10.6 | 2.6 | 6.9 | -1.9 | 1.0 | 1.6 |
| MP2/aug-cc-pVTZ | -3.9 | -3.3 | 8.6 | 18.9 | 13.4 | 12.7 | 7.9 |
Figure 2 Absolute error
Overall, MP2/6-31+G (d,p) get better results.