# Electric Field and Temperature Effects on the Ab Initio Spectroscopy of Liquid Methanol
## 3 Results and Discussion
Furthermore, whilst a temperature increase progressively broadens the CO length distribution (inset of Figure 7b), a re-entrant effect is recorded when the electric field is applied. In fact, the FWHM of the CO bond length distribution is initially widened by the field, indicating that some methanol molecules start to explore longer CO bond lengths. However, when large portions of molecules are aligned and stretched by the field, they exhibit a smaller range of (larger) CO bond lengths, as shown in Figure 7b. General effects induced either by the electric field or by the temperature on the molecular structure of bulk liquid methanol can be evaluated by means of the relevant atomistic radial distribution functions (RDFs) plotted in Figure 8. The application of an external electric field does not sizably alter the typical local structure of the first-neighboring molecules. In fact, as shown in the top panel of Figure 8 (left), neither the height nor the location of the first peak of the OO RDF are modified by the field. However, the second peak of the OO RDF moves toward shorter distances indicating that the second solvation shell is slightly compressed as the field intensity is progressively increased. As far as temperature effects on the OO RDF are concerned (Figure 8, top panel on the right), the situation is completely different. In fact, whereas the location of all peaks and dips is not affected by the temperature variation, the height of all peaks (dips) decreases (increases), manifestly indicating the de-structuring process of the H-bond network triggered by a rise in the temperature (Figure 8, top panel on the right). Similar conclusions earned from the OO RDFs can also be extracted from the intermolecular OH RDFs plotted in the central panel of Figure 8. Finally, the analysis conducted for the CO bond length is also  
Figure 6: Distributions of the lengths of the CO covalent bonds in bulk liquid methanol determined for different field strengths at room temperature **(a)** and in the absence of the external field for diverse temperatures (**b**). partially manifested from the intermolecular CO RDFs presented in the bottom panel of Figure 8. In fact, whereas the first peak of the CO RDF moves toward larger distances upon increasing the field intensity (Figure 8, bottom panel on the left), as a consequence of the field-induced molecular alignment and stretching, only a broadening and a general decrease (increase) of the peaks (dips) is observed in the CO RDFs determined for different temperatures (Figure 8, bottom panel on the right). These findings, gathered from direct atomistic evidence, magnify once again the differences observed in the vibrational response of bulk liquid methanol to the application of either an external electric field or upon varying the temperature in the absence of the field. Figure 8: _Cont._  
Figure 7: Average CO covalent bond length (**a**) and full-width at half-maximum probability of the CO covalent bond length distribution (**b**) determined as a function of the field strength. In the insets, the same quantities are determined for the zero-field case and as a function of the temperature.