Calculation of Compton Profiles Using the DV-Xα Method for 14 Electron Diatomic Molecules

AbstractUsing the Unrestricted Hartree-Fock method and supercells containing up to 160 atoms, we calculated the energy level positions in the gap and atomic geometry for the Fe4+ impurity substituting for a host Ti atom in SrTiO3. In agreement with experiment, the high spin (S=2) state is much lower in energy than the zero-spin state. The energy level positions strongly depend on the asymmetric displacement mode of the six nearest O ions which is a combination of the Jahn-Teller and breathing modes. A considerable covalent bonding between the Fe ion and four nearest O ions takes place.

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

10.26434/chemrxiv.7871504 ◽

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

10.26434/chemrxiv.7871504.v1 ◽

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.

Download Full-text