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We computed vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectra for a test set of six chiral compounds using two standard density-functionals and an array of basis sets. We analysed the performance of property-oriented basis sets using a quadruple-zeta basis as a reference against four key metrics. We find little qualitative difference between the spectra produced by the larger basis sets (ORP, LPolX, aug-cc-pVTZ, and aug-cc-pVQZ), though their quantitative metrics exhibit wide variations. The smaller basis sets (rDPS, augD-3-21G, augT3-3-21G, Sadlej-pVTZ, and aug-cc-pVDZ) performed better for VCD rotatory strengths than for the corresponding ROA circular intensity differences (CIDs). However, this trend diminishes as the basis-set size is increased, lending validity to the conclusion that more robust property-oriented basis sets are required for ROA spectral generation than that of VCD. We observed improved performance in the mid-infrared region compared to the high-frequency regime, as well as overestimation of VCD rotatory strengths in the latter region as compared to the reference. We conclude that the ORP and LPol-ds basis sets are the most efficient and effective choices of basis set for the prediction of VCD and ROA spectra, as they provide both highly accurate results at reduced computational expense. 

Real-time coupled cluster (CC) methods have several advantages over their frequency-domain counterparts, namely, response and equation of motion CC theories. Broadband spectra, strong fields, and pulse manipulation allow for the simulation of complex spectroscopies that are unreachable using frequency-domain approaches. Due to the high-order polynomial scaling, the required numerical time propagation of the CC residual expressions is a computationally demanding process. This scaling may be reduced by local correlation schemes, which aim to reduce the size of the (virtual) orbital space by truncation according to user-defined parameters. We present the first application of local correlation to real-time CC. As in previous studies of locally correlated frequency-domain CC, traditional local correlation schemes are of limited utility for field-dependent properties; however, a perturbation-aware scheme proves promising. A detailed analysis of the amplitude dynamics suggests that the main challenge is a strong time dependence of the wave function sparsity. 

Accurate modeling of the response of molecular systems to an external electromagnetic field is challenging on classical computers, especially in the regime of strong electronic correlation. In this article, we develop a quantum linear response (qLR) theory to calculate molecular response properties on near-term quantum computers. Inspired by the recently developed variants of the quantum counterpart of equation of motion (qEOM) theory, the qLR formalism employs “killer condition” satisfying excitation operator manifolds that offer a number of theoretical advantages along with reduced quantum resource requirements. We also used the qEOM framework in this work to calculate the state-specific response properties. Further, through noiseless quantum simulations, we show that response properties calculated using the qLR approach are more accurate than the ones obtained from the classical coupled-cluster-based linear response models due to the improved quality of the ground-state wave function obtained using the ADAPT-VQE algorithm.