arXiv subjects

Matúš Dubecký

Publications and source records attributed to Matúš Dubecký.

6 recordsLinked to original sources

arXiv2026

From Wavefunction Sign Structure to Static Correlation

A variational nodal partition of the correlation energy is introduced, $E_{\mathrm{cor}}=E_{\mathrm{sym}}+E_{\mathrm{stat}}$, relative to a chosen mean-field correlation baseline and its associated single-determinant node. Static correlation $E_{\mathrm{stat}}$ is the negative of the energy penalty incurred when the many-electron wavefunction is constrained to that reference node rather than the exact one. This nodal term isolates the antisymmetric, sign-structure component of correlation, while the complementary symmetric term $E_{\mathrm{sym}}$ necessarily contains dynamic correlation together with a distinct strong but nodeless contribution. The resulting state-based, method-independent framework clarifies the relation between dynamic, nondynamic, strong, and static correlation, places earlier node-based decompositions on rigorous footing, and explains why single-determinant fixed-node diffusion Monte Carlo can be highly accurate in some systems yet fail in others.

cond-mat.str-el↗

arXiv2025

Reproducibility of fixed-node diffusion Monte Carlo across diverse community codes: The case of water-methane dimer

Fixed-node diffusion quantum Monte Carlo (FN-DMC) is a widely-trusted many-body method for solving the Schrödinger equation, known for its reliable predictions of material and molecular properties. Furthermore, its excellent scalability with system complexity and near-perfect utilization of computational power makes FN-DMC ideally positioned to leverage new advances in computing to address increasingly complex scientific problems. Even though the method is widely used as a computational gold standard, reproducibility across the numerous FN-DMC code implementations has yet to be demonstrated. This difficulty stems from the diverse array of DMC algorithms and trial wave functions, compounded by the method's inherent stochastic nature. This study represents a community-wide effort to assess the reproducibility of the method, affirming that: Yes, FN-DMC is reproducible (when handled with care). Using the water-methane dimer as the canonical test case, we compare results from eleven different FN-DMC codes and show that the approximations to treat the non-locality of pseudopotentials are the primary source of the discrepancies between them. In particular, we demonstrate that, for the same choice of determinantal component in the trial wave function, reliable and reproducible predictions can be achieved by employing the T-move (TM), the determinant locality approximation (DLA), or the determinant T-move (DTM) schemes, while the older locality approximation (LA) leads to considerable variability in results. These findings demonstrate that, with appropriate choices of algorithmic details, fixed-node DMC is reproducible across diverse community codes-highlighting the maturity and robustness of the method as a tool for open and reliable computational science.

physics.comp-ph↗

arXiv2017

Bias Cancellation in One-Determinant Fixed-Node Diffusion Monte Carlo: Insights from Fermionic Occupation Numbers

Accuracy of the fixed-node diffusion Monte Carlo (FN-DMC) depends on the node location of the best available trial state $Ψ_T$. The practical FN-DMC approaches available for large systems rely on compact yet effective $Ψ_T$s containing explicitly correlated single Slater determinant (SD). However, SD nodes may be better suited to one system than to another, which may possibly lead to inaccurate FN-DMC energy differences. It remains a challenge, how to estimate inequivalency or appropriateness of SDs. Here we use the differences of a measure based on Euclidean distance between the natural orbital occupation number (NOON) vector of the Slater determinant (SD) from the exact solution in the NOON vector space, that can be viewed as a measure of SD inequivalency and a measure of the expected degree of nondynamic-correlation-related bias in FN-DMC energy differences. This is explored on a set of small noncovalent complexes and covalent bond breaking of Si$_2$ vs. N$_2$. It turns out that NOON-based measures well reflect the magnitude and sign of the bias present in the data available, thus providing new insights to the nature of bias cancellation in SD FN-DMC energy differences.

physics.chem-ph↗

arXiv2016

Noncovalent Interactions by QMC: Speedup by One-Particle Basis-Set Size Reduction

While it is empirically accepted that the fixed-node diffusion Monte-Carlo (FN-DMC) depends only weakly on the size of the one-particle basis sets used to expand its guiding functions, limits of this observation are not settled yet. Our recent work indicates that under the FN error cancellation conditions, augmented triple zeta basis sets are sufficient to achieve a benchmark level of 0.1 kcal/mol in a number of small noncovalent complexes. Here we report on a possibility of truncation of the one-particle basis sets used in FN-DMC guiding functions that has no visible effect on the accuracy of the production FN-DMC energy differences. The proposed scheme leads to no significant increase in the local energy variance, indicating that the total CPU cost of large-scale benchmark noncovalent interaction energy FN-DMC calculations may be reduced.

physics.chem-ph↗

arXiv2016

Quantum Monte Carlo for Noncovalent Interactions: An Efficient Protocol Attaining Benchmark Accuracy

Reliable theoretical predictions of noncovalent interaction energies, which are important e.g. in drug-design and hydrogen-storage applications, belong to longstanding challenges of contemporary quantum chemistry. In this respect, the fixed-node diffusion Monte Carlo (FN-DMC) is a promising alternative to the commonly used "gold standard" coupled-cluster CCSD(T)/CBS method for its benchmark accuracy and favourable scaling, in contrast to other correlated wave function approaches. This work is focused on the analysis of protocols and possible tradeoffs for FN-DMC estimations of noncovalent interaction energies and proposes an efficient yet accurate computational protocol using simplified explicit correlation terms with a favorable O(N^3) scaling. It achieves an excellent agreement (mean unsigned error ~0.2 kcal/mol) with respect to the CCSD(T)/CBS data on a number of complexes, including benzene/hydrogen,T-shape benzene dimer, stacked adenine-thymine and a set of small noncovalent complexes A24. The high accuracy and reduced computational costs predestinate the reported protocol for practical interaction energy calculations of large noncovalent complexes, where the CCSD(T)/CBS is prohibitively expensive.

physics.chem-ph↗

arXiv2014

The Work Functions of Au/Mg Decorated Au(100), Mg(001), and AuMg Alloy Surfaces: A Theoretical Study

A plane-wave density functional theory is used to predict the work functions of Au/Mg decorated Au(100), Mg(001), and stochiometric AuMg alloy surfaces. We find, that irrespective of the details, all Au/Mg systems containing Mg on the surface reveal the Mg-dominated work functions, i.e. significantly shifted toward the work function of clean Mg(001) surface. The reported analyzes suggest, that this general trend stems from a strong charge transfer from Mg to Au and consequent enhancement of a surface dipole. The calculated properties of the AuMg alloy well agree to the experiment. The reported results may readily find application in Au/Mg/AuMg surface physics and technology of metal/semiconductor contacts.

cond-mat.mtrl-sci↗