Origin-independent two-photon circular dichroism calculations in coupled cluster theory

Abstract

We present the first origin-independent approach for the treatment of two-photon circular dichroism (TPCD) using coupled cluster methods. The approach is assessed concerning its behavior on the choice of the basis set and different coupled cluster methods. We also provide a comparison of results from CC2 with those from density functional theory using the CAM-B3LYP functional. Concerning the basis set we note that in most cases an augmented triple zeta basis or a doubly augmented double zeta basis is needed for reasonably converged results. In the comparison of different coupled cluster methods results from CCSD, CC3 and CC2 have been found to be quite similar in most cases, while CCS results differ remarkably from the results at the higher levels. However, this proof-of-principle study also shows that further benchmarking of DFT and CC2 against accurate coupled cluster reference values (e.g. CCSD or CC3) is needed.

Modeling environmental effects in two-photon circular dichroism calculations

“…The term g(2ω) is the line-shape function. The two-photon circular dichroism rotatory strength involves both the electric dipole, magnetic dipole and electric quadrupole operators and it will introduce a problem of translational dependence due to the multipole origin [15,33]. However, the full velocity formulation [13] of Tinoco has been proven to be translationally invariant and thereby particularly convenient to calculate the two-photon rotational strength.…”

Cherry-Picking Resolvents: Recovering the Valence Contribution in X-ray Two-Photon Absorption within the Core–Valence-Separated Equation-of-Motion Coupled-Cluster Response Theory

“…First, we consider only the dominant electronic configuration in the initial wave function such that Ψ g ∼ Φ 0 for the CCSD state and Ψ f ∼ Φ J b for the core-excited final state. Within this simplified model, there are just four 2PA channels that need to be considered: channels (1), ( 2), (21), and ( 22) in Tables 1 and 2. Channels (1) and ( 2) are captured exactly by the CVS-0 resolvent, relative to the fc-CVS-EOM-EE-CCSD resolvent, and dominate the contributions of core-excited pre-edge states that lie below the respective core-ionization energy.…”

“…These methods are now routinely employed for computing ground- and excited-state properties in linear and nonlinear regimes. Examples of nonlinear properties include multiphoton absorption cross sections, − inelastic scattering cross sections, − first and second hyperpolarizabilities, − excited-state polarizabilities , and multiphoton transition moments between excited states, multiphoton and magnetic circular dichroism strengths, − and g -tensors, to mention just a few. In addition, the high-level CC methods provide the gold standard for benchmarking approximate and computationally less expensive methods, such as those based on density functional theory (DFT), which can treat much larger systems.…”

Probing Molecular Chirality of Ground and Electronically Excited States in the UV–vis and X-ray Regimes: An EOM-CCSD Study

“…The portfolio of spectroscopies that can be treated using EOM-CC/CC-RSP methods is vast and expanding. Spanning linear and nonlinear regimes, as well as different frequency ranges of probing radiation, it comprises UV–vis one- and two-photon absorption − and dichroism, magnetic circular dichroism, , X-ray absorption, dichroism and photoemission, , resonant inelastic X-ray scattering, ,, and many more. The non-Hermitian (bivariational) nature of the underlying formalism has initially posed some complications (compared to Hermitian variational methods) for modeling natural optical activity, but solutions have been proposed for dealing with issues such as gauge-invariance and gauge-origin dependency. , …”