Excited-State Diffusion Monte Carlo Calculations: A Simple and Efficient Two-Determinant Ansatz

Blunt, Nick S.; Neuscamman, Eric

doi:10.1021/acs.jctc.8b00879

Cited by 24 publications

(28 citation statements)

References 70 publications

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“…We used a simple single-determinant scheme to obtain the band gaps from DMC; therefore, our results should be treated as an upper bound due to the fixed node bias, which may not fully cancel between the ground and excited states. Multideterminant wavefunctions can be used to optimize the excited-state nodal surface and control fixed node bias, although studies for extended systems are very limited [131][132][133], because of the significant computational resources that would be required using DMC. A very recent work on VMC, however, shows that nodal surface errors can be minimized using orbital rotations on the singledeterminant wavefunction [134].…”

Section: Electronic Structure Quasiparticle and Optical Gapsmentioning

confidence: 99%

Structural, electronic, and magnetic properties of bulk and epitaxial LaCoO3 through diffusion Monte Carlo

Saritas

Krogel

Okamoto

et al. 2019

Phys. Rev. Materials

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Magnetism in lanthanum cobaltite (LCO, LaCoO3) appears to be strongly dependent on strain, defects, and nanostructuring. LCO on strontium titanate (STO, SrTiO3) is a ferromagnet with an interesting strain relaxation mechanism that yields a lattice modulation. However, the driving force of the ferromagnetism is still controversial. Experiments debate between a vacancy-driven or straindriven mechanism for epitaxial LCO's ferromagnetism. We found that a weak lateral modulation of the superstructure is sufficient to promote ferromagnetism. Our research also showed that ferromagnetism appears under uniaxial compression and expansion. Although earlier experiments suggest that bulk LCO is nonmagnetic, our Diffusion Monte Carlo calculations found that magnetic phases have a lower energy ground state for bulk LCO. This article discusses recent experiments indicating a more complicated picture for the bulk magnetism and closer agreement with our calculations. The role of defects are also discussed through excited-state calculations. arXiv:1908.02811v3 [cond-mat.mtrl-sci]

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Section: Electronic Structure Quasiparticle and Optical Gapsmentioning

confidence: 99%

Structural, electronic, and magnetic properties of bulk and epitaxial LaCoO3 through diffusion Monte Carlo

Saritas

Krogel

Okamoto

et al. 2019

Phys. Rev. Materials

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“…These developments also open very interesting prospects for the application of QMC to geometry relaxation in the excited state, where most electronic structure methods either lack the required accuracy or are computationally quite expensive due to their scaling with system size. To date, there are very few studies to assess the ability of QMC to predict excited-state geometries [22][23][24][25], while most of the relatively limited literature on excited-state QMC calculations is primarily concerned with vertical excitation energies [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. Importantly, all these studies are characterized by the use of very different wave functions ranging from the simple ansatz of a CI singles wave function to complete active space (CAS) expansions, sometimes truncated or only partially optimized in the presence of the Jastrow factor due to the limitations previously faced in sampling and optimizing large numbers of determinants.…”

Section: Introductionmentioning

confidence: 99%

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

Dash

Feldt

Moroni

et al. 2019

J. Chem. Theory Comput.

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We employ quantum Monte Carlo to obtain chemically accurate vertical and adiabatic excitation energies, and equilibrium excited-state structures for the small, yet challenging, formaldehyde and thioformaldehyde molecules. A key ingredient is a robust protocol to obtain balanced ground- and excited-state Jastrow–Slater wave functions at a given geometry, and to maintain such a balanced description as we relax the structure in the excited state. We use determinantal components generated via a selected configuration interaction scheme which targets the same second-order perturbation energy correction for all states of interest at different geometries, and fully optimize all variational parameters in the resultant Jastrow–Slater wave functions. Importantly, the excitation energies as well as the structural parameters in the ground and excited states are converged with very compact wave functions comprising few thousand determinants in a minimally augmented double-ζ basis set. These results are obtained already at the variational Monte Carlo level, the more accurate diffusion Monte Carlo method yielding only a small improvement in the adiabatic excitation energies. We find that matching Jastrow–Slater wave functions with similar variances can yield excitation energies compatible with our best estimates; however, the variance-matching procedure requires somewhat larger determinantal expansions to achieve the same accuracy, and it is less straightforward to adapt during structural optimization in the excited state.

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“…is observation is in agreement with the recent results of Blunt and Neuscamman on the same system. 125 As pointed out by Hammond and coworkers, 126 when the trial wave function does not include a Jastrow factor, the non-local pseudopotential can be localized analytically and the usual numerical quadrature over the angular part of the non-local pseudopotential can be eschewed. In practice, the calculation of the localized part of the pseudopotential represents only a small overhead (about 15%) with respect to a calculation without pseudopotentials (and the same number of electrons).…”

Section: Basismentioning

confidence: 99%

Influence of pseudopotentials on excitation energies from selected configuration interaction and diffusion Monte Carlo

Scemama

Caffarel

Benali

et al. 2019

Results in Chemistry

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Due to their diverse nature, the faithful description of excited states within electronic structure theory methods remains one of the grand challenges of modern theoretical chemistry.antum Monte Carlo (QMC) methods have been applied very successfully to ground state properties but still remain generally less e ective than other non-stochastic methods for electronically excited states. Nonetheless, we have recently reported accurate excitation energies for small organic molecules at the xed-node di usion Monte Carlo (FN-DMC) within a Jastrow-free QMC protocol relying on a deterministic and systematic construction of nodal surfaces using the selected con guration interaction (sCI) algorithm known as CIPSI (Con guration Interaction using a Perturbative Selection made Iteratively). Albeit highly accurate, these all-electron calculations are computationally expensive due to the presence of core electrons. One very popular approach to remove these chemically-inert electrons from the QMC simulation is to introduce pseudopotentials (also known as e ective core potentials). Taking the water molecule as an example, we investigate the in uence of Burkatzki-Filippi-Dolg (BFD) pseudopotentials and their associated basis sets on vertical excitation energies obtained with sCI and FN-DMC methods. Although these pseudopotentials are known to be relatively safe for ground state properties, we evidence that special care may be required if one strives for highly accurate vertical transition energies. Indeed, comparing all-electron and valence-only calculations, we show that using pseudopotentials with the associated basis sets can induce di erences of the order of 0.05 eV on the excitation energies. Fortunately, a reasonable estimate of this shi can be estimated at the sCI level.

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Excited-State Diffusion Monte Carlo Calculations: A Simple and Efficient Two-Determinant Ansatz

Cited by 24 publications

References 70 publications

Structural, electronic, and magnetic properties of bulk and epitaxial LaCoO3 through diffusion Monte Carlo

Structural, electronic, and magnetic properties of bulk and epitaxial LaCoO3 through diffusion Monte Carlo

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

Influence of pseudopotentials on excitation energies from selected configuration interaction and diffusion Monte Carlo

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