| 1. |
- Brumboiu, Iulia E., 1987-, et al.
(författare)
-
Analytical gradients for core-excited states in the algebraic diagrammatic construction (ADC) framework
- 2021
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 155:4
-
Tidskriftsartikel (refereegranskat)abstract
- Expressions for analytical molecular gradients of core-excited states have been derived and implemented for the hierarchy of algebraic diagrammatic construction (ADC) methods up to extended second-order within the core-valence separation (CVS) approximation. We illustrate the use of CVS-ADC gradients by determining relaxed core-excited state potential energy surfaces and optimized geometries for water, formic acid, and benzene. For water, our results show that in the dissociative lowest core-excited state, a linear configuration is preferred. For formic acid, we find that the O K-edge lowest core-excited state is non-planar, a fact that is not captured by the equivalent core approximation where the core-excited atom with its hole is replaced by the "Z + 1" neighboring atom in the periodic table. For benzene, the core-excited state gradients are presented along the Jahn-Teller distorted geometry of the 1s -> pi* excited state. Our development may pave a new path to studying the dynamics of molecules in their core-excited states.
|
|
| 2. |
- da Cruz, Vinicius Vaz, et al.
(författare)
-
Nuclear dynamics in resonant inelastic X-ray scattering and X-ray absorption of methanol
- 2019
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 150:23
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a combined theoretical and experimental study of core-excitation spectra of gas and liquid phase methanol as obtained with the use of X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). The electronic transitions are studied with computational methods that include strict and extended second-order algebraic diagrammatic construction [ADC(2) and ADC(2)-x], restricted active space second-order perturbation theory, and time-dependent density functional theory-providing a complete assignment of the near oxygen K-edge XAS. We show that multimode nuclear dynamics is of crucial importance for explaining the available experimental XAS and RIXS spectra. The multimode nuclear motion was considered in a recently developed "mixed representation" where dissociative states and highly excited vibrational modes are accurately treated with a time-dependent wave packet technique, while the remaining active vibrational modes are described using Franck-Condon amplitudes. Particular attention is paid to the polarization dependence of RIXS and the effects of the isotopic substitution on the RIXS profile in the case of dissociative core-excited states. Our approach predicts the splitting of the 2a RIXS peak to be due to an interplay between molecular and pseudo-atomic features arising in the course of transitions between dissociative core- and valence-excited states. The dynamical nature of the splitting of the 2a peak in RIXS of liquid methanol near pre-edge core excitation is shown. The theoretical results are in good agreement with our liquid phase measurements and gas phase experimental data available from the literature. (C) 2019 Author(s).
|
|
| 3. |
- Herbst, Michael F., et al.
(författare)
-
adcc : A versatile toolkit for rapid development of algebraic-diagrammatic construction methods
- 2020
-
Ingår i: Wiley Interdisciplinary Reviews. Computational Molecular Science. - : Wiley. - 1759-0876 .- 1759-0884. ; 10:6
-
Tidskriftsartikel (refereegranskat)abstract
- ADC-connect (adcc) is a hybrid python/C++ module for performing excited state calculations based on the algebraic-diagrammatic construction scheme for the polarization propagator (ADC). Key design goal is to restrict adcc to this single purpose and facilitate connection to external packages, for example, for obtaining the Hartree-Fock references, plotting spectra, or modeling solvents. Interfaces to four self-consistent field codes have already been implemented, namely pyscf, psi4, molsturm, and veloxchem. The computational workflow, including the numerical solvers, is implemented in python, whereas the working equations and other expensive expressions are done in C++. This equips adcc with adequate speed, making it a flexible toolkit for both rapid development of ADC-based computational spectroscopy methods as well as unusual computational workflows. This is demonstrated by three examples. Presently, ADC methods up to third order in perturbation theory are available in adcc, including the respective core-valence separation and spin-flip variants. Both restricted or unrestricted Hartree-Fock references can be employed.This article is categorized under: Software > Simulation Methods Electronic Structure Theory > Ab Initio Electronic Structure Methods Theoretical and Physical Chemistry > Spectroscopy Software > Quantum Chemistry
|
|
| 4. |
- Orms, Natalie, et al.
(författare)
-
Characterizing Bonding Patterns in Diradicals and Triradicals by Density-Based Wave Function Analysis : A Uniform Approach
- 2018
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 14:2, s. 638-648
-
Tidskriftsartikel (refereegranskat)abstract
- Density-based wave function analysis enables unambiguous comparisons of the electronic structure computed by different methods and removes ambiguity of orbital choices. We use this tool to investigate the performance of different spin flip methods for several prototypical diradicals and triradicals. In contrast to previous calibration studies that focused on energy gaps between high- and low spin-states, we focus on the properties of the underlying wave functions, such as the number of effectively unpaired electrons. Comparison of different density functional and wave function theory results provides insight into the performance of the different methods when applied to strongly correlated systems such as polyradicals. We show that canonical molecular orbitals for species like large copper-containing diradicals fail to correctly represent the underlying electronic structure due to highly non-Koopmans character, while density-based analysis of the same wave function delivers a clear picture of the bonding pattern.
|
|
| 5. |
- Scheurer, Maximilian, et al.
(författare)
-
Complex excited state polarizabilities in the ADC/ISR framework
- 2020
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 153:7
-
Tidskriftsartikel (refereegranskat)abstract
- We present the derivation and implementation of complex, frequency-dependent polarizabilities for excited states using the algebraic-diagrammatic construction for the polarization propagator (ADC) and its intermediate state representation. Based on the complex polarizability, we evaluate C-6 dispersion coefficients for excited states. The methodology is implemented up to third order in perturbation theory in the Python-driven adcc toolkit for the development and application of ADC methods. We exemplify the approach using illustrative model systems and compare it to results from other ab initio methods and from experiments.
|
|
| 6. |
- Scheurer, Maximilian, et al.
(författare)
-
Solving response expressions in the ADC/ISR framework
- 2023
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 158:8, s. 084105-
-
Tidskriftsartikel (refereegranskat)abstract
- We present an implementation for the calculation of molecular response properties using the algebraic-diagrammatic construction (ADC)/intermediate state representation approach. For the second-order ADC model [ADC(2)], a memory-efficient ansatz avoiding the storage of double excitation amplitudes is investigated. We compare the performance of different numerical algorithms for the solution of the underlying response equations for ADC(2) and show that our approach also strongly improves the convergence behavior for the investigated algorithms compared with the standard implementation. All routines are implemented in an open-source Python library.
|
|
| 7. |
- Scott, Mikael, et al.
(författare)
-
Ab Initio Excited-State Electronic Circular Dichroism Spectra Exploiting the Third-Order Algebraic-Diagrammatic Construction Scheme for the Polarization Propagator
- 2021
-
Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:21, s. 5132-5137
-
Tidskriftsartikel (refereegranskat)abstract
- Excited-state rotatory strengths are reported for the first time at a correlated ab initio level, here with the algebraic diagrammatic construction scheme of the polarization propagator up to the third order. To demonstrate the capabilities of this computational approach, the gas phase S-1 electronic circular dichroism spectra of the bicyclic ketones (1R)-camphor, (1R)-norcamphor, and (1R)-fenchone have been calculated at the ADC(3) level of theory. Furthermore, the solution excited-state spectra of the energetically lowest conformer of R-(+)-1,1'-bi(2-naphthol) have been computed with inclusion of a polarizable continuum model at the ADC(2) level of theory.
|
|
| 8. |
- Scott, Mikael, et al.
(författare)
-
Electronic circular dichroism spectra using the algebraic diagrammatic construction schemes of the polarization propagator up to third order
- 2021
-
Ingår i: Journal of Chemical Physics. - : AMER INST PHYSICS. - 0021-9606 .- 1089-7690. ; 154:6
-
Tidskriftsartikel (refereegranskat)abstract
- Expressions for the calculation of rotatory strengths using the algebraic diagrammatic construction (ADC) scheme of the polarization propagator in both length and velocity gauges have been implemented. This enables the simulation of electronic circular dichroism (ECD) spectra at the ADC level up to third order of perturbation theory. The ADC(n) methods produce rotatory strengths of comparable accuracy to those obtained with coupled cluster methods of corresponding approximation levels, as evaluated for methyloxirane, methylthiirane, dimethyloxirane, dimethylthiirane, hydrogen peroxide, and dihydrogen disulfide. ECD spectra of (1R)-camphor, (1R)-norcamphor, and (1R)-fenchone computed at the third order ADC(3) level of theory are shown to agree very favorably with experimental gas phase spectra, demonstrating the usefulness of ADC for the calculation of chiro-optical properties of organic molecules. ADC(2) in combination with the polarizable continuum model is shown to successfully reproduce the ECD spectrum of the L-epinephrine enantiomer in water, further demonstrating the applicability of this approach.
|
|
| 9. |
- Thielen, Sebastian M., et al.
(författare)
-
Unitary coupled-cluster approach for the calculation of core-excited states and x-ray absorption spectra
- 2021
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 154:15
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we present the core-valence separation (CVS) approximation applied to unitary coupled-cluster (UCC) theory for the calculation of core-excited states and the simulation of x-ray absorption spectroscopy (XAS). Excitation energies and oscillator strengths of small- to medium-sized organic molecules have been computed using the second-order and extended second-order UCC schemes (CVS-UCC2 and CVS-UCC2-x) as well as the third-order scheme (CVS-UCC3). All results are compared to the corresponding algebraic-diagrammatic construction methods and experimental data. The agreement between CVS-UCC and experimental data demonstrates its potential as a new approach for the calculation of XAS.
|
|
