Comparison between Optimized Geometries and Vibrational Frequencies Calculated by the DFT Methods

Abstract

Optimized geometries, vibrational frequencies, and scale factors were calculated for furan and thiophene with the HF, MP2, LDA, BVWN, BLYP, and B3LYP methods of theory using the 6-31G**, cc-pVDZ, and cc-pVTZ basis sets. The agreement between the optimized and experimental geometries was in the order B3LYP, MP2, LDA, BVWN, BLYP, then HF. The calculated frequencies by the unscaled BVWN force field had the smallest average error in the mid-IR region, but using one-scale-factor scaling, those calculated by the scaled B3LYP force field had the lowest average error. Using one-scale-factor scaling, scale factors of 0.82, 0.89, 0.98, 0.93, 0.96, and 0.96 were obtained by the HF, MP2, BLYP, B3LYP, LDA, and BVWN force fields, respectively, using the 6-31G** basis set. The effect of the basis set on the calculated bond angles, frequencies, and scale factors by the DFT methods was minor, but except with the LDA method, the agreement between the calculated and experimental bond lengths can be arranged in the order cc-pVDZ, 6-31G**, then cc-pVTZ basis set.

ATR-FTIR spectroscopic analysis of sorption of aqueous analytes into polymer coatings used with guided SH-SAW sensors

“…Vibrational frequency calculations were performed for each optimized structure and the results are summarized in Table 2 for the NO2 asymmetric stretching mode. As expected [44], the calculated frequencies deviate from experimental frequencies and a scaling factor of 0.98 was determined by comparing gas-phase experimental [28] and computational data for the vibrational mode of interest here. This scaling factor was then used to correct the rest of the computed vibrational frequencies; both unscaled and scaled data are shown in Table 2.…”

Molecular Dynamics Simulations of Proton Transport in Proton Exchange Membranes Based on Acid-Base Complexes

“…The force field models applied in this study reproduce reliable molecular configurations since the geometrical parameters are based on density functional theory at the B3LYP/6-31+G(d) level of theory. At this level of theory, the calculation errors for most bond lengths and bond angles, respectively, are within 0.02 Å and 0.6 o except a few large errors between 0.02~0.04 Å and 0.6~1.0 o (El-Azhary & Suter, 1996;Baboul, Curtiss et al, 1999). By combination of the B3LYP/6-31G(d) geometry, CHELPG residual charges, and optimized force field parameters, the force field models used in this study minimize the number of force field parameters and retains the accuracy for the description of molecular structures and hydrogen bonding.…”

Computational and Experimental Study on Molecular Structure of Benzo[g]pyrimido[4,5-b]quinoline Derivatives: Preference of Linear over the Angular Isomer

“…To study the vibrational characteristics and structural parameters of 5-(4-methoxyphenyl)-2-methylthio-5,12-dihydrobenzo[g]pyrimido [4,5-b]quinoline-4,6,11(3H)-trione 4c, we performed a theoretical study at DFT level, which allows us to set the geometric and energetic parameters of the title compound. The optimized structure with B3LYP/6-31G(d,p) level is shown in Figure 2 [46][47][48][49][50]. The calculated geometric parameter (bond lengths, bond angles and dihedral angles) at same levels of calculation for title compound was compared with the experimental parameters, see Table 3, showing very good correlation.…”