SnAu clusters as detectors of CO and NO gases: A DFT study

Where is the Hidden Intramolecular H-bonding Vibrational Signal in Proline?

“…Note that it has been shown in previous studies that with NQEs but no additional anharmonic effects, CNEO-DFT harmonic analysis already can account for most of the errors in conventional DFT harmonic analysis. 41,44,47,48 Hence, this 300 cm -1 shift relative to the DFT harmonic result is mainly due to the inclusion of NQEs through the underlying effective potential energy surface by CNEO-DFT.…”

“…48 In general, CNEO-MD will be more accurate because of the incorporation of mode coupling effects with thermal motions. 47,48 The simulated IR spectra by CNEO-MD for Type II proline and proline-D2 are provided in Figure 2(a). For both molecules, a significant band appears in the simulated spectra beginning near 2800 cm -1 .…”

“…VPT2 is a wellestablished method for anharmonic vibrational analysis, 42,43 while the CNEO theory, which was recently developed in our group, can incorporate NQEs accurately and efficiently in both quantum chemistry calculations [39][40][41] and molecular dynamics simulations. [44][45][46][47][48][49] The key difference between CNEO methods and conventional Born-Oppenheimer-based methods is that CNEO treats nuclei quantum mechanically while retaining the classical molecular geometry picture through constraints on the expectation values of nuclear position operators. 39,40 Recently, both CNEO harmonic analysis 41 and CNEO molecular dynamics (CNEO-MD) 44 have successfully been applied to a series of molecular systems with challenging hydrogen motion and/or hydrogen bonding characters, 41,44,[47][48][49] demonstrating their promise for tackling the challenge presented here with proline.…”

“…[44][45][46][47][48][49] The key difference between CNEO methods and conventional Born-Oppenheimer-based methods is that CNEO treats nuclei quantum mechanically while retaining the classical molecular geometry picture through constraints on the expectation values of nuclear position operators. 39,40 Recently, both CNEO harmonic analysis 41 and CNEO molecular dynamics (CNEO-MD) 44 have successfully been applied to a series of molecular systems with challenging hydrogen motion and/or hydrogen bonding characters, 41,44,[47][48][49] demonstrating their promise for tackling the challenge presented here with proline. Here, with both CNEO harmonic and VPT2 analyses, we will provide strong evidence supporting the original assignment of the Type II hydrogen bonded O-H stretch as appearing close to the C-H stretching region, and with CNEO-MD, we will further validate this assignment by reproducing the experimental difference spectrum.…”

“…[51][52][53] The PBE0 [54][55][56] electronic functional was adopted in all calculations as it has been shown to give accurate vibrational results for hydrogen-bonded systems. 47,48 The aug-cc-pVDZ basis set was used for electrons, 57 while the PB4-D basis was used for protons. 58 For CNEO-MD simulations, we use the direct NVE scheme that our group recently introduced for efficient spectrum calculations.…”