Absorption Properties of Large Complex Molecular Systems: The DFTB/Fluctuating Charge Approach

Abstract

We report on the first formulation of a novel polarizable QM/MM approach, where the density functional tight binding (DFTB) is coupled to the fluctuating charge (FQ) force field. The resulting method (DFTB/FQ) is then extended to the linear response within the TD-DFTB framework and challenged to study absorption spectra of large condensed-phase systems.

UV-Resonance Raman Spectra of Systems in Complex Environments: A Multiscale Modeling Applied to Doxorubicin Intercalated into DNA

“…Those molecular orbitals are all localized on the anthraquinone moiety. − Using CAM-B3LYP and QM/FQ, the vertical excitation energy for solvated DOX is reported to be 431 nm in ref . From simulations using DFTB/FQ, there are some shifts in the calculated spectra with respect to the experimental ones . By using an electrostatic embedding to treat the environment (see also Figure S3 in the SI), the absorption maximum of DOX intercalated in DNA lies at 497 nm and at 477 nm for DOX in water (B3LYP/DZP level of theory).…”

“…From simulations using DFTB/FQ, there are some shifts in the calculated spectra with respect to the experimental ones. 46 By using an electrostatic embedding to treat the environment (see also Figure S3 in the SI ), the absorption maximum of DOX intercalated in DNA lies at 497 nm and at 477 nm for DOX in water (B3LYP/DZP level of theory). To correctly reproduce the experimental conditions, we use shifted excitations as incident wavelengths in the simulation of the RR spectra.…”

“…Details of the equations employed to compute cross sections are described in Section S4 of the SI. Excitation wavelengths for RR are chosen based on DFTB/FQ UV–vis spectra already reported by some of us . Simulated spectra are generated by convoluting RR peaks with a Lorentzian band shape with a half-width at half maximum of 10 cm –1 .…”

“…Excitation wavelengths for RR are chosen based on DFTB/FQ UV–vis spectra already reported by some of us. 46 Simulated spectra are generated by convoluting RR peaks with a Lorentzian band shape with a half-width at half maximum of 10 cm –1 . To obtain the final RR spectra, the resulting individual spectra are averaged.…”

“…DOX is part of the anthracycline anticancer group, and it has been claimed that this drug binds with DNA via an intercalation mechanism. , Figure displays an intercalation complex between DOX and DNA. Drug/DNA complexes have been computationally studied, and some works − are listed in Table S1 in the Supporting Information (SI).…”