Variational and diffusion quantum Monte Carlo calculations with the CASINO code

Needs, R. J.; Towler, M. D.; Drummond, Neil; Ríos, Pablo López; Trail, J. R.

doi:10.1063/1.5144288

Cited by 123 publications

(92 citation statements)

References 240 publications

(369 reference statements)

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“…We describe the trial wave functions and the form of the single-particle orbitals used to calculate the ground-state energy of the EEBW system. We have used the casino [60] code to perform VMC calculations.…”

Section: Methodsmentioning

confidence: 99%

Ground-state properties of electron-electron biwire systems

et al. 2021

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The correlation between electrons in different quantum wires is expected to affect the electronic properties of quantum electron-electron biwire systems. Here, we use the variational Monte Carlo method to study the ground-state properties of parallel, infinitely thin electron-electron biwires for several electron densities (rs) and interwire separations (d). Specifically, the ground-state energy, the correlation energy, the interaction energy, the pair-correlation function (PCF), the static structure factor (SSF), and the momentum distribution (MD) function are calculated. We find that the interaction energy increases as ln(d) for d → 0 and it decreases as d −2 when d → ∞. The PCF shows oscillatory behavior at all densities considered here. As two parallel wires approach each other, interwire correlations increase while intrawire correlations decrease as evidenced by the behavior of the PCF, SSF, and MD. The system evolves from two monowires of density parameter rs to a single monowire of density parameter rs/2 as d is reduced from infinity to zero. The MD reveals Tomonaga-Luttinger (TL) liquid behavior with a power-law nature near kF even in the presence of an extra interwire interaction between the electrons in biwire systems. It is observed that when d is reduced the MD decreases for k < kF and increases for k > kF, similar to its behavior with increasing rs. The TL liquid exponent is extracted by fitting the MD data near kF, from which the TL liquid interaction parameter Kρ is calculated. The value of the TL parameter is found to be in agreement with that of a single wire for large separation between the two wires.

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Section: Methodsmentioning

confidence: 99%

Ground-state properties of electron-electron biwire systems

et al. 2021

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“…In non-covalent interactions, the challenge for FN-DMC is to provide precise and accurate evaluations of the interaction energy E int , despite E int being a tiny fraction of the total energy, e.g., it is circa 1/10 4 of the total energy in the C 60 @ [6]CPPA complex. Precision is achieved by exploiting the almost perfect scaling of DMC on modern supercomputer facilities [42][43][44] and thanks to recent algorithmic improvements which reduced the time-step bias and made DMC up to 100 times more efficient 40 . The FN-DMC setup here employed has been used and validated against experiments and CCSD(T) a number of times, for instance in refs.…”

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confidence: 99%

Interactions between large molecules pose a puzzle for reference quantum mechanical methods

et al. 2021

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Quantum-mechanical methods are used for understanding molecular interactions throughout the natural sciences. Quantum diffusion Monte Carlo (DMC) and coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] are state-of-the-art trusted wavefunction methods that have been shown to yield accurate interaction energies for small organic molecules. These methods provide valuable reference information for widely-used semi-empirical and machine learning potentials, especially where experimental information is scarce. However, agreement for systems beyond small molecules is a crucial remaining milestone for cementing the benchmark accuracy of these methods. We show that CCSD(T) and DMC interaction energies are not consistent for a set of polarizable supramolecules. Whilst there is agreement for some of the complexes, in a few key systems disagreements of up to 8 kcal mol−1 remain. These findings thus indicate that more caution is required when aiming at reproducible non-covalent interactions between extended molecules.

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“…Speeding up QMC simulations has been an important focus in computational chemistry. Various software packages have been developed to this end [26,35,43]. For instance, Kim et al [26] demonstrated how DMC algorithms can be efficiently implemented on high-performance computer clusters.…”

Section: Introductionmentioning

confidence: 99%