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In this paper, we report on the implementation of CC2 and CC3 in the context of molecules in finite magnetic fields. The methods are applied to the investigation of atoms and molecules through spectroscopic predictions and geometry optimizations for the study of the atmospheres of highly-magnetized White Dwarfs (WDs). We show that ground-state finite-field (ff) CC2 is a reasonable alternative to CCSD for energies and, in particular for geometrical properties. For excited states ff-CC2 is shown to perform well for states with predominant single-excitation character. Yet, for cases in which the excited-state wavefunction has double-excitation character with respect to the reference, ff-CC2 can easily Ff-CC3, however, is shown to reproduce the CCSDT behaviour very well and enables the treatment of larger systems at a high accuracy.

The development of efficient techniques to distinguish mirror images of chiral molecules (enantiomers) is very important in both chemistry and physics. Enantiomers share most molecular properties except, for instance, the absorption of circularly polarized light. Enantiomer purification is therefore a challenging task that requires specialized equipment. Strong coupling between quantized fields and matter (e.g. in optical cavities) is a promising technique to modify molecular processes in a non-invasive way. The modulation of molecular properties is achieved by changing the field characteristics. In this work, we investigate whether strong coupling to circularly polarized electromagnetic fields is a viable way to discriminate chiral molecules. To this end, we develop a nonperturbative framework to calculate the behavior of molecules in chiral cavities. We show that in this setting the enantiomers have different energies -- that is, one is more stable than the other. The field-induced energy differences are also shown to give rise to enantiospecific signatures in rotational spectra., Comment: 18 pages and 14 figures

The fully polarizable QM/MM approach based on fluctuating charges and fluctuating dipoles, named QM/FQF{\mu} (J. Chem. Theory Comput. 2019, 15, 2233-2245), is extended to the evaluation of nuclear gradients and the calculation of IR spectra of molecular systems in condensed phase. To this end, analytical equations defining first and second energy derivatives with respect to nuclear coordinates are derived and discussed. The potentialities of the approach are shown by applying the model to the calculation of IR spectra of Methlyoxirane, Glycidol and Gallic Acid in aqueous solution. The results are compared with the continuum QM/PCM and the polarizable QM/FQ, which is based on Fluctuating Charges only., Comment: 42 pages, 11 figures