scholarly journals A New and Efficient Equation-of-Motion Coupled-Cluster Framework for Core-Excited and Core-Ionized States

2019 ◽  
Author(s):  
Marta Lopez Vidal ◽  
Xintian Feng ◽  
Evgeny Epifanovsky ◽  
Anna Krylov ◽  
Sonia Coriani
Keyword(s):  
Reference Data ◽  
Equation Of Motion ◽  
Basis Set ◽  
Target Space ◽  
Coupled Cluster ◽  
Ionization Energies ◽  
The Core ◽  
Core Approximation ◽  
Spectral Intensities ◽  
Experimental Reference

We present a fully analytical implementation of the core-valence separation (CVS) scheme for the equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) method for calculations of core-level states. In the spirit of the original CVS approximation proposed by Cederbaum, Domcke and Schirmer, pure valence excitations are excluded from the EOM target space and the frozen-core approximation is imposed on the reference-state amplitudes and multipliers. This yields an efficient, robust, and accurate EOM-CCSD framework for calculations of excitation and ionization energies as well as state and transition properties (e.g., spectral intensities, natural transition and Dyson orbitals). The accuracy of the new scheme is improved relative to the results obtained applying the CVS only during the solution of the EOM eigenvalue equations. The errors in absolute excitation/ionization energies relative to the experimental reference data are of the order of 0.2{3.0 eV, depending on the K-edge considered and on the basis set used, and the shifts are systematic for each edge.<br>

scholarly journals A New and Efficient Equation-of-Motion Coupled-Cluster Framework for Core-Excited and Core-Ionized States

2018 ◽  
Author(s):  
Marta Lopez Vidal ◽  
Xintian Feng ◽  
Evgeny Epifanovsky ◽  
Anna Krylov ◽  
Sonia Coriani
Keyword(s):  
Reference Data ◽  
Equation Of Motion ◽  
Basis Set ◽  
Target Space ◽  
Coupled Cluster ◽  
Ionization Energies ◽  
The Core ◽  
Core Approximation ◽  
Spectral Intensities ◽  
Experimental Reference

We present a fully analytical implementation of the core-valence separation (CVS) scheme for the equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) method for calculations of core-level states. In the spirit of the original CVS approximation proposed by Cederbaum, Domcke and Schirmer, pure valence excitations are excluded from the EOM target space and the frozen-core approximation is imposed on the reference-state amplitudes and multipliers. This yields an efficient, robust, and accurate EOM-CCSD framework for calculations of excitation and ionization energies as well as state and transition properties (e.g., spectral intensities, natural transition and Dyson orbitals). The accuracy of the new scheme is improved relative to the results obtained applying the CVS only during the solution of the EOM eigenvalue equations. The errors in absolute excitation/ionization energies relative to the experimental reference data are of the order of 0.2{3.0 eV, depending on the K-edge considered and on the basis set used, and the shifts are systematic for each edge.<br>

scholarly journals A New and Efficient Equation-of-Motion Coupled-Cluster Framework for Core-Excited and Core-Ionized States

2019 ◽  
Author(s):  
Marta Lopez Vidal ◽  
Xintian Feng ◽  
Evgeny Epifanovsky ◽  
Anna Krylov ◽  
Sonia Coriani
Keyword(s):  
Reference Data ◽  
Equation Of Motion ◽  
Basis Set ◽  
Target Space ◽  
Coupled Cluster ◽  
Ionization Energies ◽  
The Core ◽  
Core Approximation ◽  
Spectral Intensities ◽  
Experimental Reference

We present a fully analytical implementation of the core-valence separation (CVS) scheme for the equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) method for calculations of core-level states. In the spirit of the original CVS approximation proposed by Cederbaum, Domcke and Schirmer, pure valence excitations are excluded from the EOM target space and the frozen-core approximation is imposed on the reference-state amplitudes and multipliers. This yields an efficient, robust, and accurate EOM-CCSD framework for calculations of excitation and ionization energies as well as state and transition properties (e.g., spectral intensities, natural transition and Dyson orbitals). The accuracy of the new scheme is improved relative to the results obtained applying the CVS only during the solution of the EOM eigenvalue equations. The errors in absolute excitation/ionization energies relative to the experimental reference data are of the order of 0.2{3.0 eV, depending on the K-edge considered and on the basis set used, and the shifts are systematic for each edge.<br>

scholarly journals A New and Efficient Equation-of-Motion Coupled-Cluster Framework for Core-Excited and Core-Ionized States

2019 ◽  
Author(s):  
Marta Lopez Vidal ◽  
Xintian Feng ◽  
Evgeny Epifanovsky ◽  
Anna Krylov ◽  
Sonia Coriani
Keyword(s):  
Reference Data ◽  
Equation Of Motion ◽  
Basis Set ◽  
Target Space ◽  
Coupled Cluster ◽  
Ionization Energies ◽  
The Core ◽  
Core Approximation ◽  
Spectral Intensities ◽  
Experimental Reference

We present a fully analytical implementation of the core-valence separation (CVS) scheme for the equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) method for calculations of core-level states. In the spirit of the original CVS approximation proposed by Cederbaum, Domcke and Schirmer, pure valence excitations are excluded from the EOM target space and the frozen-core approximation is imposed on the reference-state amplitudes and multipliers. This yields an efficient, robust, and accurate EOM-CCSD framework for calculations of excitation and ionization energies as well as state and transition properties (e.g., spectral intensities, natural transition and Dyson orbitals). The accuracy of the new scheme is improved relative to the results obtained applying the CVS only during the solution of the EOM eigenvalue equations. The errors in absolute excitation/ionization energies relative to the experimental reference data are of the order of 0.2{3.0 eV, depending on the K-edge considered and on the basis set used, and the shifts are systematic for each edge.<br>

scholarly journals Towards the Search for Thallium Nuclear Schiff Moment in Polyatomic Molecules: Molecular Properties of Thallium Monocyanide (TlCN)

Atoms ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 62 ◽  
Author(s):  
A. Kudrin ◽  
A. Zaitsevskii ◽  
T. Isaev ◽  
D. Maison ◽  
L. Skripnikov
Keyword(s):  
Inner Core ◽  
Molecular Properties ◽  
Basis Set ◽  
Cluster Method ◽  
Coupled Cluster ◽  
The Core ◽  
Complete Basis Set ◽  
Core Electrons ◽  
Complete Basis Set Limit ◽  
Potential Energy Minimum

Molecular properties of the thallium monocyanide (Tl·CN) system in its ground electronic state are studied using high-precision ab initio relativistic two-component pseudopotential replacing 60 inner-core electrons of Tl. A relativistic coupled-cluster method with single, double and perturbative triple amplitudes is employed to account for electronic correlations. Extrapolation of results to the complete basis set limit is used for all studied properties. The global potential energy minimum of Tl·CN corresponds to the linear cyanide (TlCN) isomer, while the non-rigid isocyanide-like (TlNC) structure lies by approximately 11 kJ/mol higher in energy. The procedure of restoration of the wavefunction in the “core” region of Tl atom was applied to calculate the interaction of the Tl nuclear Schiff moment with electrons. The parameter X of the interaction of the Tl nuclear Schiff moment with electrons in the linear TlCN molecule equals 7150 a.u. The prospects of using the TlCN molecule for the experimental detection of the nuclear Schiff moment are discussed.

scholarly journals Dyson orbitals within the fc-CVS-EOM-CCSD framework: theory and application to X-ray photoelectron spectroscopy of ground and excited states

2020 ◽  
Vol 22 (5) ◽  
pp. 2693-2703 ◽  
Author(s):  
Marta L. Vidal ◽  
Anna I. Krylov ◽  
Sonia Coriani
Keyword(s):  
Excited States ◽  
Photoelectron Spectroscopy ◽  
Equation Of Motion ◽  
Coupled Cluster ◽  
Ionization Energies ◽  
X Ray

Ionization energies and Dyson orbitals within frozen-core core–valence separated equation-of-motion coupled cluster singles and doubles (fc-CVS-EOM-CCSD) enable efficient and reliable calculations of standard XPS and of UV-pump/XPS probe spectra.

A Case Study of State-Specific and State-Averaged Brueckner Equation-of-Motion Coupled-Cluster Theory: The Ionic-Covalent Avoided Crossing in Lithium Fluoride

2005 ◽  
Vol 70 (8) ◽  
pp. 1082-1108 ◽  
Author(s):  
Marcel Nooijen ◽  
K. R. Shamasundar
Keyword(s):  
Molecular System ◽  
Solution Process ◽  
Iterative Solution ◽  
Equation Of Motion ◽  
The State ◽  
Basis Set ◽  
Coupled Cluster ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Avoided Crossing

State-specific Brueckner equation-of-motion coupled-cluster theory (SS-B-EOMCC) is summarized, which can be considered an internally contracted version of a state-selective multireference coupled-cluster theory, which, however, is not entirely size-consistent. The method is applicable to general multireference problems, adheres to the space and spin symmetries of the molecular system, is straightforwardly extended to a state-averaged version, and has an associated perturbative variant which yields results close to the full coupled-cluster treatment. A key strength is that Brueckner orbitals are used, such that orbitals are optimized in the presence of dynamic correlation. A number of variations on the theme of SS-EOMCC is applied to study the ionic-covalent avoided crossing in LiF in a 6-311++G(3df,3pd) basis set. While reasonable results are obtained at the state-averaged level, the iterative solution process does not consistently converge for SS-EOMCC, due to the non-Hermiticity of the transformed Hamiltonian which may yield complex eigenvalues upon truncated diagonalization. This leads to an irrevocable breakdown of the state-specific EOMCC approach. We indicate some future directions that can resolve some of the problems with the SS-EOMCC methodology, as revealed by the demanding test case of the LiF potential energy curves.

A Multi-Layer Approach to the Equation of Motion Coupled-Cluster Method for the Electron Affinity

2020 ◽  
Author(s):  
Soumi Haldar ◽  
Achintya Kumar Dutta
Keyword(s):  
Electron Affinity ◽  
Electron Attachment ◽  
Equation Of Motion ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Large Molecules ◽  
Layer Method ◽  
Speed Up ◽  
Attachment Process

We have presented a multi-layer implementation of the equation of motion coupled-cluster method for the electron affinity, based on local and pair natural orbitals. The method gives consistent accuracy for both localized and delocalized anionic states. It results in many fold speedup in computational timing as compared to the canonical and DLPNO based implementation of the EA-EOM-CCSD method. We have also developed an explicit fragment-based approach which can lead to even higher speed-up with little loss in accuracy. The multi-layer method can be used to treat the environmental effect of both bonded and non-bonded nature on the electron attachment process in large molecules.<br>

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