scholarly journals Excited States with Selected Configuration Interaction-Quantum Monte Carlo: Chemically Accurate Excitation Energies and Geometries

2019 ◽  
Vol 15 (9) ◽  
pp. 4896-4906 ◽  
Author(s):  
Monika Dash ◽  
Jonas Feldt ◽  
Saverio Moroni ◽  
Anthony Scemama ◽  
Claudia Filippi
Keyword(s):  
Monte Carlo ◽  
Excited States ◽  
Configuration Interaction ◽  
Quantum Monte Carlo ◽  
Excitation Energies

Modification of HAM/3 excitation energies for ΠΠ* transitions of linear molecules

1980 ◽  
Vol 58 (16) ◽  
pp. 1687-1690 ◽  
Author(s):  
Delano P. Chong
Keyword(s):  
Excitation Energy ◽  
Explicit Expression ◽  
Excited States ◽  
Configuration Interaction ◽  
Excitation Energies ◽  
Carbon Suboxide ◽  
Numerical Examples ◽  
Energy Correction ◽  
Linear Molecules ◽  
Configuration Interaction Calculations

The excitation energies calculated by the HAM/3 procedure for ΠΠ* transitions in linear molecules can be internally inconsistent by as much as ± 0.6 eV. In the recent study by Åsbrink etal., the problem was avoided by adopting Recknagel's expressions and requiring the proper average ΠΠ* excitation energy. In this paper, we trace the small inconsistency back to its origin in HAM/3 theory and derive the analytical expression for the energy correction as well as Recknagel's formulas. Numerical examples studied include all seven linear molecules investigated by Åsbrink etal. The explicit expression for the correction enables us to perform meaningful configuration-interaction calculations on the excited states, as illustrated by the carbon suboxide molecule.

scholarly journals Low-Cost Molecular Excited States from a State-Averaged Resonating Hartree-Fock Approach

2019 ◽  
Author(s):  
Jacob Nite ◽  
Carlos A. Jimenez-Hoyos
Keyword(s):  
Excited States ◽  
Configuration Interaction ◽  
Low Cost ◽  
Computational Cost ◽  
Mean Field ◽  
Chem Phys ◽  
Spin Projection ◽  
Excitation Energies ◽  
Hartree Fock ◽  
Orbital Relaxation

Quantum chemistry methods that describe excited states on the same footing as the ground state are generally scarce. In previous work, Gill et al. (J. Phys. Chem. A 112, 13164 (2008)) and later Sundstrom and Head-Gordon (J. Chem. Phys. 140, 114103 (2014)) considered excited states resulting from a non-orthogonal configuration interaction (NOCI) on stationary solutions of the Hartree–Fock equations. We build upon those contributions and present the state-averaged resonating Hartree–Fock (sa-ResHF) method, which differs from NOCI in that spin-projection and orbital relaxation effects are incorporated from the onset. Our results in a set of small molecules (alanine, formaldehyde, acetaldehyde, acetone, formamide, and ethylene) suggest that sa-ResHF excitation energies are a notable improvement over configuration interaction singles (CIS), at a mean-field computational cost. The orbital relaxation in sa-ResHF, in the presence of a spin-projection operator, generally results in excitation energies that are closer to the experimental values than the corresponding NOCI ones.

scholarly journals Low-Cost Molecular Excited States from a State-Averaged Resonating Hartree-Fock Approach

2019 ◽  
Author(s):  
Jacob Nite ◽  
Carlos A. Jimenez-Hoyos
Keyword(s):  
Excited States ◽  
Configuration Interaction ◽  
Low Cost ◽  
Computational Cost ◽  
Mean Field ◽  
Chem Phys ◽  
Spin Projection ◽  
Excitation Energies ◽  
Hartree Fock ◽  
Orbital Relaxation

Quantum chemistry methods that describe excited states on the same footing as the ground state are generally scarce. In previous work, Gill et al. (J. Phys. Chem. A 112, 13164 (2008)) and later Sundstrom and Head-Gordon (J. Chem. Phys. 140, 114103 (2014)) considered excited states resulting from a non-orthogonal configuration interaction (NOCI) on stationary solutions of the Hartree–Fock equations. We build upon those contributions and present the state-averaged resonating Hartree–Fock (sa-ResHF) method, which differs from NOCI in that spin-projection and orbital relaxation effects are incorporated from the onset. Our results in a set of small molecules (alanine, formaldehyde, acetaldehyde, acetone, formamide, and ethylene) suggest that sa-ResHF excitation energies are a notable improvement over configuration interaction singles (CIS), at a mean-field computational cost. The orbital relaxation in sa-ResHF, in the presence of a spin-projection operator, generally results in excitation energies that are closer to the experimental values than the corresponding NOCI ones.

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