Vibrational Circular Dichroism from DFT Molecular Dynamics: The AWV Method

Abstract

The paper illustrates the Activity Weighted Velocities (AWV) methodology to compute Vibrational Circular Dichroism (VCD) anharmonic spectra from Density Functional Theory (DFT) molecular dynamics. AWV calculates the spectra by the Fourier Transform of the time correlation functions of velocities, weighted by specific observables: the Atomic Polar Tensors (APTs) and the Atomic Axial Tensors (AATs). Indeed, AWV shows to correctly reproduce the experimental spectra for systems in the gas and liquid phases, both in the case of weakly and strongly interacting systems. The comparison with the experimental spectra is striking especially in the fingerprint region, as demonstrated by the three benchmark systems discussed: (1S)-Fenchone in the gas phase, (S)-(−)-Propylene oxide in the liquid phase, and (R)-(−)-2-butanol in the liquid phase. The time evolution of APTs and AATs can be adequately described by a linear combination of the tensors of a small set of appropriate reference structures, strongly reducing the computational cost without compromising accuracy. Additionally, AWV allows the partition of the spectral signal in its molecular components without any expensive postprocessing and any localization of the charge density or the wave function.

Selective Chirality Transfer to the Bis(trifluoromethylsulfonyl)imide Anion of an Ionic Liquid

“…In Figure 1 (top black spectrum) we show the validity of our approach by the simulated VCD spectrum of an isolated ( R )‐PO molecule in the gas phase. This spectrum compares excellent with experimental data [26,28] and previously calculated spectra from AIMD simulations [42] and quantum chemical calculations [26,28,47] . There is a pronounced bisignate pattern between 850 cm −1 to 1000 cm −1 , a negative peak at around 1120 cm −1 , and a (−/+) signal between 1250 cm −1 to 1400 cm −1 in the gas phase.…”

“…This spectrum compares excellent with experimental data [26,28] and previously calculated spectra from AIMD simulations [42] and quantum chemical calculations. [26,28,47] There is a pronounced bisignate pattern between 850 cm À 1 to 1000 cm À 1 , a negative peak at around 1120 cm À 1 , and a (À / +) signal between 1250 cm À 1 to 1400 cm À 1 in the gas phase. Compared to that, the total spectrum of the (R)-PO@IL system (grey spectrum in Figure 1) looks very different and is dominated by a (+ /À / + /À / +) pattern between 1055 cm À 1 to 1127 cm À 1 .…”

Efficient Prediction of Mole Fraction Related Vibrational Frequency Shifts

“…( R )-Butan-2-ol molecules form homodromic structures and interact mainly through OH···O hydrogen bonds and dispersion interactions between the hydrocarbon chains (see Figure , top right). Liquid phase IR and VCD spectra of ( R )-butan-2-ol have been investigated by cluster weighting , and ab initio molecular dynamics , before, and we were able to reproduce these results with the cluster set employed herein (see Figures S2 and S3, Table S1, and the corresponding discussion in the Supporting Information). These successful applications to neat liquids justify the application of the cluster weighting approach for the calculation of mole fraction dependent liquid phase spectra of mixtures.…”

Vibrational Circular Dichroism Spectroscopy of Chiral Molecular Crystals: Insights from Theory

“…Galimberti showed recently that the dynamic picture can be combined with the tensor representation in Equation (4) using activity-weighted velocities. [53] The TCF furthermore replaces the normal mode analysis, which can be tedious for big systems that exhibit a large number of supramolecular interactions and shallow potential energy surfaces whose anharmonic parts are significantly populated. [54,55] In the following, a general notation is used for both representations, static or dynamic,…”

“…This representation is especially suited for VCD computations based on MD simulations, because the instantaneous moments can be obtained directly from MD trajectories. Galimberti showed recently that the dynamic picture can be combined with the tensor representation in Equation (4) using activity‐weighted velocities [53] . The TCF furthermore replaces the normal mode analysis, which can be tedious for big systems that exhibit a large number of supramolecular interactions and shallow potential energy surfaces whose anharmonic parts are significantly populated [54, 55] .…”