Relativistic effects on magnetic circular dichroism studied by GUHF/SECI method

Efficient Calculation of Magnetic Circular Dichroism Spectra Using Spin-Noncollinear Linear-Response Time-Dependent Density Functional Theory in Finite Magnetic Fields

Excited-state calculations in finite magnetic fields are presented in the framework of spin-noncollinear linear-response time-dependent density functional theory. To ensure gauge-origin invariance, London atomic orbitals are employed throughout. An efficient implementation into the Turbomole package, which also includes the resolution of the identity approximation, allows for the investigation of excited states of large molecular systems. The implementation is used to investigate the magnetic circular dichroism spectra of sizable organometallic molecules such as a zinc tetraazaporphyrin with two fused naphthalene units, which is a molecule with 57 atoms.

Comparison of standard and damped response formulations of magnetic circular dichroism

We apply damped response theory to the phenomenon of magnetic circular dichroism (MCD), and we investigate how the numerical instability associated with the simulation of the MCD spectrum from individually calculated A and B terms for close lying states can be remedied by the use of damped response theory. We also present a method for calculating the Faraday A term, formulated as a double residue of the quadratic response function.

Multireference ab initio studies of zero-field splitting and magnetic circular dichroism spectra of tetrahedral Co(II) complexes

A newly developed multireference (MR) ab initio method for the calculation of magnetic circular dichroism (MCD) spectra was calibrated through the calculation of the ground- and excited state properties of seven high-spin (S = 3/2) Co(II) complexes. The MCD spectra were computed by the explicit treatment of spin-orbit coupled (SOC) and spin-spin coupled (SSC) N-electron states. For the complexes studied in this work, we found that the SOC is more important than the SSC for determining the ground state zero field splitting (ZFS). Our computed ZFS parameter D for the [Co(PPh(3))(2)Cl(2)] model complex is -17.6 cm(-1), which is reasonably close to the experimental value of -14.8 cm(-1). Generally, the computed absorption and MCD spectra are in fair agreement with experiment for all investigated complexes. Thus, reliable electronic structure and spectroscopic predictions for medium sized transition metal complexes are feasible on the basis of this methodology. This characterizes the presented method as a promising tool for MCD spectra interpretations of transition metal complexes in a variety of areas of chemistry and biology.

Theoretical studies on magnetic circular dichroism by the finite perturbation method with relativistic corrections

A theoretical method for calculating magnetic circular dichroism (MCD) of molecules is presented. We examined the numerical accuracy and the stability of the finite perturbation (FP) method and the sum-over-state (SOS) perturbation method. The relativistic effects are shown to be important for the MCD spectra of molecules containing heavy elements. Calculations using the FP and the SOS methods were carried out for ethylene, para- and ortho-benzoquinone, showing that the FP method is superior to the SOS method, as expected. The relativistic effect was examined using the second-order Douglas-Kroll Hamiltonians for the halogen molecules F2, Cl2, Br2, and I2. The Faraday terms of I2 and Br2 were strongly affected by the relativistic effects, while the effect was negligible for Cl2 and F2.

Calculation of the A term of magnetic circular dichroism based on time dependent-density functional theory I. Formulation and implementation

A procedure for calculating the A term and the A/D ratio of magnetic circular dichroism (MCD) within time-dependent density functional theory (TD-DFT) is described. Utilizing an implementation of the MCD theory within the Amsterdam Density Functional program, the A term contributions to the MCD spectra of MnO(4) (-), CrO(4) (2-), VO(4) (3-), MoO(4) (2-), VO(4) (3-), MoS(4) (2-), Se(4) (2+), Te(4) (2+), Fe(CN)(6) (4-), Ni(CN)(4) (2-), trichlorobenzene, hexachlorobenzene, tribromobenzene, and hexabromobenzene are calculated. For the most part, agreement between theory and experiment for A/D ratios and the relative magnitude of A terms is found to be good, leading to simulated spectra that are similar in appearance to those derived from measurements. The A terms are found to be too small whenever comparison with experiment was possible, probably due to the neglect of environment effects on the incident radiation and the relative low accuracy of dipole strengths calculated within TD-DFT.