Implementation and Application of the Frozen Density Embedding Theory with the Algebraic Diagrammatic Construction Scheme for the Polarization Propagator up to Third Order

Implementation, benchmarking, and representative applications of the new FDE-ADC(3) method for describing environmental effects on excited states as a combination of frozen density embedding (FDE) and the algebraic-diagrammatic construction scheme for the polarization propagator of third order (ADC(3)) are presented. Results of FDE-ADC(3) calculations are validated with respect to supersystem calculations on test systems with varying molecule–environment interaction strengths from dispersion up to multiple hydrogen bonds. The overall deviation compared to the supersystem calculations is as small as 0.029 eV for excitation energies, which is even smaller than the intrinsic error of ADC(3). The dependence of the accuracy on the choice of method and functional for the calculation of the environment and the nonelectrostatic part of the system–environment interaction is evaluated. In three representative examples, the FDE-ADC method is applied to investigate larger systems and to analyze excited state properties using visualization of embedded densities and orbitals

Utilizing the 8‑Methoxycyclooct-4-en-1-ide Unit As a Hydrogen Atom Acceptor en Route to “Metal–Borane Pincers”

The synthesis and characterization of palladium and platinum complexes containing the neutral ligand HB­(mp)₂ (where mp = 2-mercaptopyridyl) are presented. Addition of 2 equiv of Na­[H₂B­(mp)₂] to [M­(Cl)­(COE^OMe)]₂ (where M = Pt, Pd; COE^OMe = 8-methoxycyclooct-4-en-1-ide) in the presence of 2 equiv of PPh₃ leads to the formation of the metal–borane pincer complexes [Pt­{κ³<i>SBS</i>-HB­(mp)₂}­(PPh₃)] and [Pd­{κ³<i>SBS</i>-HB­(mp)₂}­(PPh₃)]. In these reactions, a hydrogen migration reaction occurs from the borohydride ligand to the metal center, eventually leading to the elimination of the COE^OMe unit from the metal center. X-ray crystallographic characterization of the two isostructural complexes reveals a rare <i>mer</i>-κ³<i>S</i>,<i>B</i>,<i>S</i> coordination mode with short platinum– and palladium–boron distances: 2.098(4) and 2.091(3) Å, respectively (the shorter distances of two independent complexes in the unit cells of both structures). The complexes [Pd­{κ³<i>S</i>,<i>B</i>,<i>S</i>-HB­(mp)₂}­(PPh₃)] and [Pt­{κ³<i>S</i>,<i>B</i>,<i>S</i>-HB­(mp)₂}­(PPh₃)] are the first examples of metal–borane complexes featuring a pincer-type coordination where one hydrogen substituent remains at the boron center

Benchmark of Excitation Energy Shifts from Frozen-Density Embedding Theory: Introduction of a Density-Overlap-Based Applicability Threshold

We present a thorough investigation of the errors in results obtained with the combination of frozen-density embedding theory and the algebraic diagrammatic construction scheme for the polarization propagator of second order (FDE-ADC(2)). The study was carried out on a set of 52 intermolecular complexes with varying interaction strength, each consisting of a chromophore of fundamental interest and a few small molecules in its environment. The errors emerging in frozen-density embedding theory-based methods originate from (a) the solver of the quantum many-body problem used to obtain the embedded wave function (Ψ_A^emb), (b) the approximation for the explicit density functional for the embedding potential, and (c) the choice of the density representing the environment (ρ_B(<i>r⃗</i>)). The present work provides a comprehensive analysis of the errors in the excitation energies based on the last two factors. Furthermore, a density-overlap-based parameter is proposed to be used as an a priori criterion of applicability

OpenMolcas: From source code to insight

In this article we describe the OpenMolcas environment and invite the computational chemistry community to collaborate. The open-source project already includes a large number of new developments realized during the transition from the commercial MOLCAS product to the open-source platform. The paper initially describes the technical details of the new software development platform. This is followed by brief presentations of many new methods, implementations, and features of the OpenMolcas program suite. These developments include novel wave function methods such as stochastic complete active space self-consistent field, density matrix renormalization group (DMRG) methods, and hybrid multiconfigurational wave function and density functional theory models. Some of these implementations include an array of additional options and functionalities. The paper proceeds and describes developments related to explorations of potential energy surfaces. Here we present methods for the optimization of conical intersections, the simulation of adiabatic and nonadiabatic molecular dynamics and interfaces to tools for semiclassical and quantum mechanical nuclear dynamics. Furthermore, the article describes features unique to simulations of spectroscopic and magnetic phenomena such as the exact semiclassical description of the interaction between light and matter, various X-ray processes, magnetic circular dichroism and properties. Finally, the paper describes a number of built-in and add-on features to support the OpenMolcas platform with post calculation analysis and visualization, a multiscale simulation option using frozen-density embedding theory and new electronic and muonic basis sets