Implementation and validation of a multi-purpose virtual spectrometer for large systems in complex environments

Abstract

Despite impressive advances of computational spectroscopy, a robust and user-friendly multi-frequency virtual spectrometer is not yet available. This contribution summarises ongoing efforts in our research group toward the implementation and validation of such a tool with special reference to the building blocks of biomolecules in their natural environment. Our integrated computational tool allows the computation of several kinds of spectra, including vibrational (e.g. IR, VCD), electronic (e.g. absorption, emission, ECD) as well as magnetic resonance (e.g. ESR, NMR) for both closed- and open-shell systems in vacuo and in condensed phases, and includes facilities for drawing, comparing, and modifying all the computed spectra. A number of test cases involving a combination of different spectroscopic ranges will be discussed in order to point out strengths, limitations, and ongoing developments of our research plan.

Anharmonic theoretical simulations of infrared spectra of halogenated organic compounds

“…In fact, although the original N07D provided very good results in the computation of frequencies and EPR properties, 29,35,44,52,[58][59][60]71,72,[78][79][80][81] the inclusion of diffuse functions and pseudopotentials are needed to properly treat the heaviest halogen atoms and to improve the performances of the IR intensity calculations. The double-hybrid B2PLYP 84,85 functional, along with its analytic second derivatives 50 required for the effective computation of semi-diagonal quartic force-fields, was also employed in conjunction with the cc-pVTZ basis set (cc-pVTZ-PP in case of Br and I).…”

“…In the last years, theoretical computations have become powerful and widespread tools for the assignment and prediction of the experimental spectra, as well as to get deeper insight into the different effects which determine the observed spectroscopic properties. [26][27][28][29] As far as IR spectroscopy is concerned, QM calculations carried out at a suitable level of theory allow the prediction of reliable vibrational spectra for small-to medium-sized molecules (for example see Refs. 21,[30][31][32][33][34][35][36] and references therein) In this respect, while approaches based on the vibrational perturbation theory (VPT2) 33,34,[37][38][39][40][41][42] have been shown capable of accurately calculating vibrational frequencies, comparatively less attention has been paid to infrared intensities beyond the double-harmonic approximation.…”

Validation of a computational protocol to simulate near IR phosphorescence spectra for Ru(II) and Ir(III) metal complexes

“…[Ru(bpy) 3 ] 2+ , has been recently investigated as a test case for the prediction and analysis of resonance Raman (RR) spectra of inorganic complexes by one of us [16]. In this study, it has been shown that the recent implementation of the so-called virtual multifrequency spectrometer (VMS) [35,36] offers a powerful and cheap tool for RR predictions, even when one includes a large number of effects (solvent, anharmonicity and Duschinsky couplings) modulating the spectra. Last year we used the VMS to perform simulations in order to reproduce the phosphorescence spectra of three ruthenium terpyridine derivatives to evaluate the reliability of our tool [37].…”

Vibronic coupling to simulate the phosphorescence spectra of Ir(III)-based OLED systems: TD-DFT results meet experimental data

“…Then, in order to plot the phosphorescence spectra, vibronic contributions to electronic emission have been considered using the Adiabatic Shift (AS) approach as implemented in the used version of the Gaussian Package. [42,70] The optimized geometries and vibration frequencies of the first triplet state have been obtained using unrestricted calculations. Spin-orbit coupling and Herzberg-Teller terms have not been taken into account in the calculations.…”

“…[41] The computation of the vibrational structure of electronic absorption or emission bands should permit to reproduce more accurately both the position and the band shape of the observed spectra. In this context, Barone and coworkers implemented recently the so called Virtual Multifrequency Spectrometer (VMS) [42,43] which is a powerful, mature and cheap tool to simulate accurately many types of spectra, even when one aims to investigate large systems or a large number of effects (solvent, anharmonicity and Duschinsky couplings). [50][51][52][53][54][55][56][57][58][59] Indeed, in the last years, the VMS approach has been used to simulate with high precision anharmonic and phosphorescence spectra of organometallics and transition metal complexes.…”