The advent of attosecond techniques opens up the possibility to observe experimentally electron dynamics following ionization molecules. Theoretical studies pure at single fixed nuclear geometries in molecules have demonstrated oscillatory charge migration a well-defined frequency but often neglecting natural width wave packet. effect on spatial delocalization nuclei is an outstanding question. Here, we show how inherent distribution leads dephasing. Using simple analytical model,...

The M4,5-edge high energy resolution X-ray absorption near-edge structure (HR-XANES) spectra of actinyls offer valuable insights into the electronic and bonding properties heavy-element complexes. To conduct a comprehensive spectral analysis, it is essential to employ computational methods that accurately account for relativistic effects electron correlation. In this work, we utilize variational multireference configurational interaction compute analyze M4-edge spectrum uranyl. By employing...

The multiconfiguration nature of late-row (≥4th) elements and their molecular complexes, combined with significant relativistic effects, present large challenges for the accurate description electronic structure. To address these incorporate both electron correlation we a two-component Kramers-unrestricted multireference configuration interaction method where effects are included variationally at orbital level via use "exact two-component" transformation solution one-electron modified Dirac...

As the relativistic corrections become stronger for late-row elements, fully perturbative treatment of spin-orbit coupling and dynamic correlation may inadequate accurate descriptions chemical properties. In this work, we introduce a determinant-based Kramers-unrestricted exact-two-component multireference second-order perturbation (X2C-MRPT2) method which variationally includes with correlation. The restricted active space partitioning scheme is employed to provide an adjustable treatment....

The complex nature of the f-orbital electronic structures and their interaction with chemical environment pose significant computational challenges. Advanced techniques that variationally include scalar relativities spin–orbit coupling directly at molecular orbital level have been developed to address this complexity. Among these, variational relativistic multiconfigurational multireference methods stand out for high accuracy systematic improvement in studies f-block complexes. Additionally,...

The modeling of spin–orbit coupling (SOC) remains a challenge in computational chemistry due to the high cost. With rising popularity spin-driven processes and f-block metals materials science, it is incumbent on community develop accurate multiconfigurational SOC methods that scale large systems understand limits different treatments SOC. Herein, we introduce an implementation perturbative scalar-relativistic two-component CASSCF (srX2C-CASSCF-SO). Perspectives limitations accuracy...

An algorithm is described for quantum dynamics where an Ehrenfest potential combined with fully nuclear motion (Quantum-Ehrenfest, Qu-Eh). The method related to the single-set variational multi-configuration Gaussian approach (vMCG) but has advantage that only a single chemistry computation required at each time step since there time-dependent surface. Also shown close relationship "exact factorization method." compared vMCG study of electron in modified bismethylene-adamantane cation...

Molecules containing late-row elements exhibit large relativistic effects. To account for both effects and electron correlation in a computationally inexpensive way, we derived formulation of multiconfiguration pair-density functional theory with the exact-two-component Hamiltonian (X2C-MC-PDFT). In this new method, are included during variational optimization reference wave function by complete active-space self-consistent-field (X2C-CASSCF) theory, followed an energy evaluation using...

The accurate description of the electronic structure transition metals and their compounds can be complicated by both large number close-lying states that often have multiconfigurational nature significant relativistic effects. In order to address these challenges we present a two-component complete-active-space self-consistent field method includes scalar effects one-electron spin–orbit coupling during wave function optimization procedure. These are included via an "exact two-component"...

The theoretical prediction of x-ray absorption spectra (XAS) has become commonplace in electronic structure theory. ability to better model and understand L-edge is great interest the study transition metal complexes a wide variety solid state materials. However, until recently few first-principles works have modeled XAS due presence strong spin–orbit coupling 2p orbitals, which splits observed peaks into multiple groups features. Therefore, proper description vital for successful spectra. A...

In photochemical processes, spin-orbit coupling plays a crucial role in determining the outcome of reaction. However, exact treatment Dirac-Coulomb-Breit two-electron operator required for rigorous inclusion is computationally prohibitive. To address this challenge, we present Dirac-Coulomb-Breit-parameterized screened-nuclear factor to approximate couplings effective one-electron Hamiltonian. We propose two schemes, universal and row-dependent parameterizations, further improve accuracy...

We simulate electron dynamics following ionization in 2-phenyl-ethyl-amine and 2-phenylethyl-N,N-dimethylamine as examples of systems where 3 coupled cationic states are involved. study two nuclear effects on dynamics: (i) electron-nuclear motion (ii) spatial delocalization a result the zero-point energy neutral molecule. Within Ehrenfest approximation, our calculations show that coherent these molecules is not lost motion. In contrast, delocalization, dephasing oscillations occurs time...

We have simulated the coupled electron and nuclear dynamics using Ehrenfest method upon valence ionisation of modified bismethylene-adamantane (BMA) molecules where there is an transfer between two π bonds. shown that motion significantly affects after a few fs when electronic states involved are close in energy. also demonstrated how non-stationary wave packet determines motion, more precisely asymmetric stretching bonds, illustrating “charge-directed reactivity”. Taking into account width...

The observation of electronic motion remains a key target in the development field attoscience. However, systems which long-lived oscillatory charge migration may be observed must selected carefully, particularly because it has been shown that nuclear spatial delocalization leads to loss coherent electron density oscillations. Here we demonstrate dynamics norbornadiene and extended where hole migrates between two identical chromophores. By studying effect these example systems, present...

Electron correlation and environmental effects play important roles in electron dynamics spectroscopic observables of chemical systems condensed phase. In this paper, we present a time-dependent complete active space configuration interaction (TD-CASCI) approach embedded polarizable force field, MMPol. The implementation TD-CASCI/MMPol utilizes direct matrix-vector contraction, allowing studies large systems. This scheme is used to study the solvatochromic shift coumarin 153 methanol....

Despite the power and flexibility of configuration interaction (CI) based methods in computational chemistry, their broader application is limited by an exponential increase both storage requirements, particularly due to substantial memory needed for excitation lists that are crucial scalable parallel computing. The objective this work develop a new CI framework, namely, small tensor product distributed active space (STP-DAS) aimed at drastically reducing demands extensive calculations on...

We demonstrate that charge migration can be ‘engineered’ in arbitrary molecular systems if a single localised orbital – diabatically follows nuclear displacements is ionised. Specifically, we describe the use of natural bonding orbitals Complete Active Space Configuration Interaction (CASCI) calculations to form cationic states with charge, providing consistently well-defined initial conditions across zero point energy vibrational ensemble geometries. In Ehrenfest dynamics simulations...

X-ray absorption spectroscopy is a powerful probe of local electronic and nuclear structures, providing insights into chemical processes. The theoretical prediction interpretation metal L-edge spectra are complicated by both relativistic effects, including spin-orbit coupling the multiconfigurational nature states involved. This work details an exact two-component multireference restricted active space (RAS) configuration interaction scheme that uses state-averaged complete...

Without rigorous symmetry constraints, solutions to approximate electronic structure methods may artificially break symmetry. In the case of relativistic structure, if time-reversal is not enforced in calculations molecules subject a magnetic field, it possible Kramers degeneracy open shell systems. This leads description excited states that be qualitatively incorrect. Despite this, different incorporate correlation and can partially restore from broken solution. For single-reference...

The radiolysis of liquid water and the radiation-matter interactions that happen in aqueous environments are important to fields chemistry, materials, environmental sciences, as well biological physiological response extreme conditions medical treatments. initial stage is ultrafast response, or hole dynamics, triggers chemical processes within complex energetic landscapes may include reactivity. A fundamental understanding necessitates use theoretical methods capable simulating both...

Density functional theory (DFT) has been a cornerstone in computational chemistry, physics, and materials science for decades, benefiting from advancements power theoretical methods. This paper introduces novel, cloud-native application, Accelerated DFT, which offers an order of magnitude acceleration DFT simulations. By integrating state-of-the-art cloud infrastructure redesigning algorithms graphic processing units (GPUs), achieves high-speed calculations without sacrificing accuracy. It...

We present a theoretical study of intersystem crossing (ISC) in acrolein and ketene with the Ehrenfest method that can describe superposition singlet triplet states. Our simulations illustrate new mechanistic effect ISC, namely, singlets triplets yields nonadiabatic dynamics characteristic rather than constituent state potential energy surfaces. This is particularly significant ketene, where mixing states along approach to singlet/singlet conical intersection occurs, spin–orbit coupling...

An implementation of the Ehrenfest method with damped velocity is discussed. The then applied to study non-adiabatic reaction paths for two simple chemical systems: isomerization allene radical cation in its excited state and channel 3 photochemical transformation benzene benzvalene. For both systems initial conditions trajectory were either an adiabatic eigenstate geometry close a conical intersection, or superposition eigenstates at intersection. In we able show that reaction, which passes...