arXiv subjects

Erin R. Johnson

Publications and source records attributed to Erin R. Johnson.

7 recordsLinked to original sources

arXiv2026

Performance of a minimally empirical local-hybrid density functional for molecular chemistry

Delocalisation error has been argued to be the greatest outstanding challenge in density-functional theory (DFT). One of the most promising routes to minimise this error is development of local hybrid functionals, in which the fraction of exact-exchange mixing is position dependent. However, existing local hybrids capable of good thermochemical accuracy are often highly empirical, and tend to have complicated functional forms that involve some combination of range separation, calibration functions, power-series expansions, or even neural networks. In this work, we explore the limits of what can be achieved with a minimally empirical local hybrid functional form that avoids such complexities. The ``LHnz'' functional is proposed, which uses dispersionless exchange and a local mixing fraction dependent on the correlation length and effective exchange--correlation hole normalisations. With only three empirical parameters, LHnz is shown to outperform all existing global hybrid functionals for the GMTKN55 molecular-thermochemistry benchmark with no large outliers.

physics.chem-ph↗

arXiv2026

Consistent GMTKN55 and molecular-crystal accuracy using minimally empirical DFT with XDM(Z) dispersion

Density-functional theory (DFT) has become the workhorse of modern computational chemistry, with dispersion corrections such as the exchange-hole dipole moment (XDM) model playing a key role in high-accuracy modelling of large-scale systems. All previous production implementations of XDM have used the two-parameter Becke--Johnson damping function based on atomic radii. Here, we introduce and implement a new XDM variant that uses a one-parameter damping function based on atomic numbers, recently proposed by Becke. Both this new Z damping and the canonical BJ-damping variants of XDM are benchmarked on the comprehensive GMTKN55 database using minimally empirical generalised-gradient-approximation, global hybrid, and range-separated hybrid functionals. This marks the first time that the XDM (and many-body dispersion, MBD) corrections have been tested on the GMTKN55 set. Using the new WTMAD-4 metric, an outlier analysis is performed for all new data, as well as for top-ranking functionals from the literature at each rung, providing insight into both performance and consistency across the dataset. We also extended our analysis to the DM21 and Skala machine-learned functionals that have garnered recent attention. To test Z damping's transferability to the solid state, four benchmarks involving molecular crystals are also considered. Across these molecular and solid-state benchmarks, the revPBE0 and B86bPBE0 hybrid functionals, paired with the Z-damped XDM variant, show excellent performance.

physics.chem-ph↗

arXiv2026

The effects of dispersion damping and three-body interactions for accurate layered-material exfoliation energies

Accurate predictions of exfoliation energies and lattice constants of layered materials hinge on a correct description of London dispersion physics. Modern a posteriori dispersion corrections in density-functional theory (DFT), such as the exchange-hole dipole moment (XDM) model, capture the proper asymptotic behaviour at long range while making use of damping functions to prevent unphysical divergence at short range. In the united-atom limit, the dispersion energy is damped to a finite, non-zero value by both the canonical Becke--Johnson (BJ) damping function and the new Z-damping function. XDM(BJ) has previously demonstrated exceptional accuracy for modelling layered materials, such as in the LM26 benchmark, which includes graphite, hexagonal boron nitride, lead(II) oxide, and transition-metal dichalcogenides. This work presents the first assessment of XDM(Z) on the same benchmark. We also show that inclusion of three-body interactions via the Axilrod--Teller--Muto (ATM) term further improves the computed exfoliation energies for both XDM(BJ) and XDM(Z), yielding the best performance achieved on LM26 using semi-local functionals to date, relative to reference data from the random-phase approximation.

cond-mat.mtrl-sci↗

arXiv2026

Roadmap on Advancements of the FHI-aims Software Package

Electronic-structure theory is the foundation of the description of materials including multiscale modeling of their properties and functions. Obviously, without sufficient accuracy at the base, reliable predictions are unlikely at any level that follows. The software package FHI-aims has proven to be a game changer for accurate free-energy calculations because of its scalability, numerical precision, and its efficient handling of density functional theory (DFT) with hybrid functionals and van der Waals interactions. It treats molecules, clusters, and extended systems (solids and liquids) on an equal footing. Besides DFT, FHI-aims also includes quantum-chemistry methods, descriptions for excited states and vibrations, and calculations of various types of transport. Recent advancements address the integration of FHI-aims into an increasing number of workflows and various artificial intelligence (AI) methods. This Roadmap describes the state-of-the-art of FHI-aims and advancements that are currently ongoing or planned.

cond-mat.mtrl-sci↗

arXiv2025

WTMAD-4: A Fair Weighting Scheme for GMTKN55

The GMTKN55 data set is a collection of standard benchmarks used in molecular quantum chemistry that spans small- and large-molecule thermochemistry, reaction barriers, and non-covalent interactions. Herein, we identify a flaw in the weighted mean absolute deviation (WTMAD) definitions commonly used to quantify performance of various electronic-structure methods for the GMTKN55 set, which under-weight some of its component benchmarks by orders of magnitude. A new WTMAD-4 metric is proposed, based on typical errors observed for a set of ten minimally empirical dispersion-corrected density-functional approximations (DFAs), ensuring fair treatment across all benchmarks. The performance of 115 DFAs is then reassessed using WTMAD-4 and we highlight a literature example where a DFA parametrised by minimising WTMAD-2 underperforms for benchmarks marginalised by that metric.

physics.chem-ph↗

arXiv2022

A deep Aurum reservoir: Stable compounds of two bulk-immiscible metals under pressure

The Earth's crust is known to be depleted of gold, among other slightly heavy noble metals transported by magma from the Earth's mantle to the crust. The bulk silicate Earth (BSE) model also suggests significant depletion of Au in the silicate mantle itself, which cannot be explained by the amount of Au in the mantle's magma. This implies that Au could remain in the lower mantle and form stable compounds, especially with iron, which is the predominant element within the core. While Fe does not form binary compounds or a bulk alloy with Au under ambient conditions, it may do so at the elevated pressures found in the Earth's interior. Here, using density-functional methods, we investigated the possibility of identifying stable, binary Fe-Au compounds at pressures up to 210 GPa. We found three such Fe-Au compounds, which are stabilized by pressure and notable electron transfer, including an orthorhombic AuFe$_4$ phase that is ferromagnetic in nature with Au possessing a significant magnetic moment. While our results suggest that thermal convection due to the conductivities and the heat flux from the Fe-Au compounds could be an energy source to power the Earth's geodynamo, they also point towards changes in Au's chemical properties, as it can exist as either an anion or cation under pressure. In addition, the sound velocity and the density predicted for the various Fe-Au compounds suggest that they could shed light on the composition of the core-mantle boundary and the Earth's core, while demonstrating how the presence of trace amounts of Au could influence agreement with seismic data.

cond-mat.mtrl-sci↗

arXiv2014

Global empirical potentials from purely rotational measurements

The recent advent of chirped-pulse FTMW technology has created a plethora of pure rotational spectra for molecules for which no vibrational information is known. The growing number of such spectra demands a way to build empirical potential energy surfaces for molecules, without relying on any vibrational measurements. Using ZnO as an example, we demonstrate a powerful technique for efficiently accomplishing this. We first measure eight new ultra-high precision ($\pm2$ kHz) pure rotational transitions in the $X$-state of ZnO. Combining them with previous high-precision ($\pm50$ kHz) pure rotational measurements of different transitions in the same system, we have data that spans the bottom 10\% of the well. Despite not using any vibrational information, our empirical potentials are able to determine the size of the vibrational spacings and bond lengths, with precisions that are more than three and two orders of magnitude greater, respectively, than the most precise empirical values previously known, and the most accurate \emph{ab initio} calculations in today's reach. By calculating the $C_{6},$ $C_{8},$ and $C_{10}$ long-range constants and using them to anchor the top of the well, our potential is \emph{globally} in excellent agreement with \emph{ab initio} calculations, without the need for vibrational spectra and without the need for \emph{any} data in the top 90\% of the well.

physics.chem-ph↗