20 research outputs found
Modeling the absorption spectrum of the permanganate ion in vacuum and in aqueous solution
The absorption spectrum of the MnO ion has been a test-bed for
quantum-chemical methods over the last decades. Its correct description
requires highly-correlated multiconfigurational methods, which are incompatible
with the inclusion of finite-temperature and solvent effects due to their high
computational demands. Therefore, implicit solvent models are usually employed.
Here we show that implicit solvent models are not sufficiently accurate to
model the solvent shift of MnO, and we analyze the origins of their
failure. We obtain the correct solvent shift for MnO in aqueous
solution by employing the polarizable embedding (PE) model combined with a
range-separated complete active space short-range density functional theory
method (CAS-srDFT). Finite-temperature effects are taken into account by
averaging over structures obtained from ab initio molecular dynamics
simulations. The explicit treatment of finite-temperature and solvent effects
facilitates the interpretation of the bands in the low-energy region of the
MnO absorption spectrum, whose assignment has been elusive.Comment: 15 pages, 3 tables, 1 Figur
Investigating the influence of relativistic effects on absorption spectra for platinum complexes with light-activated activity against cancer cells
We report the first investigation of relativistic effects on the UV-vis
spectra of two prototype complexes for so-called photo-activated chemotherapy
(PACT), trans-trans-trans-[Pt(N3)2(OH)2(NH3)2] and
cis-trans-cis-[Pt(N3)2(OH)2(NH3)2].In PACT, design of new drugs requires
in-depth understanding of the photo-activation mechanisms. A first step is
usually to rationalize their UV-vis spectra for which time-dependent density
functional theory (TD-DFT) is an indispensable tool. We carried out TD-DFT
calculations with a systematic series of non-relativistic(NR),
scalar-relativistic (SR), and four-component (4c) Hamiltonians. Large
differences are found between spectra calculated within 4c and NR frameworks,
while the most intense features (found at higher energies below 300 nm) can be
reasonably well reproduced within a SR framework. Yet the underlying
transitions can be strongly influenced by spin-orbit coupling introduced in the
4c framework: while this can affect both intense and less intense transitions
in the spectra, the effect is most pronounced for weaker transitions at lower
energies, above 300 nm. Since the investigated complexes are activated with
light of wavelengths above 300 nm, employing a method with explicit inclusion
of spin-orbit coupling may be crucial to rationalize the activation mechanism.
All calculations were carried out with both the CAM-B3LYP and B3LYP
functionals; we generally find the former to perform best in comparison with
experimental spectra.Comment: 24 pages, 10 Figures, 1 Table. 25 pages supporting informatio
Multiconfigurational Short-Range Density-Functional Theory for Open-Shell Systems
Many chemical systems cannot be described by quantum chemistry methods based
on a singlereference wave function. Accurate predictions of energetic and
spectroscopic properties require a delicate balance between describing the most
important configurations (static correlation) and obtaining dynamical
correlation efficiently. The former is most naturally done through a
multiconfigurational (MC) wave function, whereas the latter can be done by,
e.g., perturbation theory. We have employed a different strategy, namely, a
hybrid between multiconfigurational wave functions and density-functional
theory (DFT) based on range separation. The method is denoted by MC short-range
(sr) DFT and is more efficient than perturbative approaches as it capitalizes
on the efficient treatment of the (short-range) dynamical correlation by DFT
approximations. In turn, the method also improves DFT with standard
approximations through the ability of multiconfigurational wave functions to
recover large parts of the static correlation. Until now, our implementation
was restricted to closed-shell systems, and to lift this restriction, we
present here the generalization of MC-srDFT to open-shell cases. The additional
terms required to treat open-shell systems are derived and implemented in the
DALTON program. This new method for open-shell systems is illustrated on
dioxygen and [Fe(H2O)6]3+.Comment: 37 pages, 3 figures, 4 tables, 1 appendix and 79 references Changes
in v2: 1) Appendix B and reference 81 removed 2) Removed dublicated reference
and corrected reference 31. 3) Added spin-charge cross terms to GGA (Appendix
A). Code changed accordingly and GGA results recalculated. All GGA results
are revised -only small modifications observed. Conclusions are unchange
Density Matrix Renormalization Group with Efficient Dynamical Electron Correlation Through Range Separation
We present a new hybrid multiconfigurational method based on the concept of
range-separation that combines the density matrix renormalization group
approach with density functional theory. This new method is designed for the
simultaneous description of dynamical and static electron-correlation effects
in multiconfigurational electronic structure problems.Comment: 13 pages, 4 figures, 2 table
New Approaches for ab initio Calculations of Molecules with Strong Electron Correlation
Reliable quantum chemical methods for the description of molecules with
dense-lying frontier orbitals are needed in the context of many chemical
compounds and reactions. Here, we review developments that led to our
newcomputational toolbo x which implements the quantum chemical density matrix
renormalization group in a second-generation algorithm. We present an overview
of the different components of this toolbox.Comment: 19 pages, 1 tabl
The DIRAC code for relativistic molecular calculations
DIRAC is a freely distributed general-purpose program system for one-, two-, and four-component relativistic molecular calculations at the level of Hartree?Fock, Kohn?Sham (including range-separated theory), multiconfigurational self-consistent-field, multireference configuration interaction, electron propagator, and various flavors of coupled cluster theory. At the self-consistent-field level, a highly original scheme, based on quaternion algebra, is implemented for the treatment of both spatial and time reversal symmetry. DIRAC features a very general module for the calculation of molecular properties that to a large extent may be defined by the user and further analyzed through a powerful visualization module. It allows for the inclusion of environmental effects through three different classes of increasingly sophisticated embedding approaches: the implicit solvation polarizable continuum model, the explicit polarizable embedding model, and the frozen density embedding model.Fil: Saue, Trond. UniversitĂ© Paul Sabatier; Francia. Centre National de la Recherche Scientifique; FranciaFil: Bast, Radovan. Uit The Arctic University Of Norway; NoruegaFil: Gomes, AndrĂ© Severo Pereira. University Of Lille.; Francia. Centre National de la Recherche Scientifique; FranciaFil: Jensen, Hans Jorgen Aa.. University of Southern Denmark; DinamarcaFil: Visscher, Lucas. Vrije Universiteit Amsterdam; PaĂses BajosFil: Aucar, Ignacio AgustĂn. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Nordeste. Instituto de Modelado e InnovaciĂłn TecnolĂłgica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e InnovaciĂłn TecnolĂłgica; Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de FĂsica; ArgentinaFil: Di Remigio, Roberto. Uit The Arctic University of Norway; NoruegaFil: Dyall, Kenneth G.. Dirac Solutions; Estados UnidosFil: Eliav, Ephraim. Universitat Tel Aviv.; IsraelFil: Fasshauer, Elke. Aarhus University. Department of Bioscience; DinamarcaFil: Fleig, Timo. UniversitĂ© Paul Sabatier; Francia. Centre National de la Recherche Scientifique; FranciaFil: Halbert, LoĂŻc. Centre National de la Recherche Scientifique; Francia. University Of Lille.; FranciaFil: HedegĂ„rd, Erik Donovan. Lund University; SueciaFil: Helmich-Paris, Benjamin. Max-planck-institut FĂŒr Kohlenforschung; AlemaniaFil: Ilias, Miroslav. Matej Bel University; EslovaquiaFil: Jacob, Christoph R.. Technische UniversitĂ€t Braunschweig; AlemaniaFil: Knecht, Stefan. Eth ZĂŒrich, Laboratorium FĂŒr Physikalische Chemie; SuizaFil: Laerdahl, Jon K.. Oslo University Hospital; NoruegaFil: Vidal, Marta L.. Department Of Chemistry; DinamarcaFil: Nayak, Malaya K.. Bhabha Atomic Research Centre; IndiaFil: Olejniczak, Malgorzata. University Of Warsaw; PoloniaFil: Olsen, JĂłgvan Magnus Haugaard. Uit The Arctic University Of Norway; NoruegaFil: Pernpointner, Markus. Kybeidos Gmbh; AlemaniaFil: Senjean, Bruno. Universiteit Leiden; PaĂses BajosFil: Shee, Avijit. Department Of Chemistry; Estados UnidosFil: Sunaga, Ayaki. Tokyo Metropolitan University; JapĂłnFil: van Stralen, Joost N. P.. Vrije Universiteit Amsterdam; PaĂses Bajo
A method to capture the large relativistic and solvent effects on the UV-vis spectra of photo-activated metal complexes
We have recently developed a method based on relativistic time-dependent density functional theory (TD-DFT) that allows the calculation of electronic spectra in solution (Creutzberg, HedegÄrd, J. Chem. Theory Comput.18, 2022, 3671). This method treats the solvent explicitly with a classical, polarizable embedding (PE) description. Furthermore, it employs the complex polarization propagator (CPP) formalism which allows calculations on complexes with a dense population of electronic states (such complexes are known to be problematic for conventional TD-DFT). Here, we employ this method to investigate both the dynamic and electronic effects of the solvent for the excited electronic states of trans-trans-trans-[Pt(N3)2(OH)2(NH3)2] in aqueous solution. This complex decomposes into species harmful to cancer cells under light irradiation. Thus, understanding its photo-physical properties may lead to a more efficient method to battle cancer. We quantify the effect of the underlying structure and dynamics by classical molecular mechanics simulations, refined with a subsequent DFT or semi-empirical optimization on a cluster. Moreover, we quantify the effect of employing different methods to set up the solvated system, e.g., how sensitive the results are to the method used for the refinement, and how large a solvent shell that is required. The electronic solvent effect is always included through a PE potential
New relativistic quantum chemical methods for understanding light-induced therapeutics
The inorganic platinum complexes currently in clinical use for cancer treatment have severe side effects, and complexes with fewer side effects are required. One option is to use complexes that are inactive until they are light-activated. Theoretical chemistry can contribute to the design of these complexes, but most current theoretical methods lack explicit treatment of relativistic effects (since the target complexes often contain heavy elements). In particular, spin-orbit coupling is required for accurate predictions of the complexesâ photo-physical properties. In this perspective, we summarize relativistic methods developed in recent years that can contribute to our understanding of light-induced reactivity and thereby help predict new, suitable complexes