The ever-growing availability of computing power and the sustained development of advanced computational methods have contributed much to recent scientific progress. These developments present new challenges driven by the sheer amount of calculations and data to manage. Next-generation exascale supercomputers will harden these challenges, such that automated and scalable solutions become crucial. In recent years, we have been developing AiiDA (aiida.net), a robust open-source high-throughput infrastructure addressing the challenges arising from the needs of automated workflow management and data provenance recording. Here, we introduce developments and capabilities required to reach sustained performance, with AiiDA supporting throughputs of tens of thousands processes/hour, while automatically preserving and storing the full data provenance in a relational database making it queryable and traversable, thus enabling high-performance data analytics. AiiDA’s workflow language provides advanced automation, error handling features and a flexible plugin model to allow interfacing with external simulation software. The associated plugin registry enables seamless sharing of extensions, empowering a vibrant user community dedicated to making simulations more robust, user-friendly and reproducible.

The lattice dynamics of potassium dihydrogen phosphate (KDP) and its deuterated analog DKDP was studied via first-principles DFT calculations. A thorough assessment of the quality of a wide range of functionals supplemented with the approximate inclusion of quantum nuclear effects indicated that the non-local van der Waals functional vdW-DF [M. Dion et al, Phys. Rev. Lett. 92, 246401 (2004); J. Klimeš et al, Phys. Rev. B 83, 195131 (2011)] produces the best agreement with structural data for both compounds. This enabled the calculation of full phonon dispersions in the ferroelectric phase, and hence the phonon density of states and specific heat, in excellent agreement with experimental data. Phonon bands and especially modes at the Γ-point of the Brillouin zone were classified according to their vibrational pattern. This allowed for the assignment of stretching and bending modes of the hydrogen bonds. Internal modes involving the phosphate units were identified at lower frequencies, while the lowest-lying modes were those involving the K + ion. These assignments were used to interpret infrared and Raman spectra along the c-axis, and in the perpendicular plane. Phonon modes calculated at the Γ-point showed two types of instabilities. One was a normal mode polarized along the c-axis of the crystal, while the other corresponded to a twofold degenerate mode polarized in the perpendicular plane. The former gives rise to a spontaneous polarization in the ferroelectric phase at low temperatures by coupling to an optical K +-PO − 4 stretching mode, consistently with a significant off-diagonal Born effective charge on the hydrogen atoms. A mode describing the opposite rotation of neighboring PO4 tetrahedra was also found to couple strongly to the ferroelectric mode, as this modulates the O-O distance, which determines the barrier for proton transfer. The present study suggests that a minimal model to describe isotope effects in KDP should involve at least three fully-coupled vibrational modes.

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The prediction of material properties based on density-functional theory has become routinely common, thanks, in part, to the steady increase in the number and robustness of available simulation packages. This plurality of codes and methods is both a boon and a burden. While providing great opportunities for cross-verification, these packages adopt different methods, algorithms, and paradigms, making it challenging to choose, master, and efficiently use them. We demonstrate how developing common interfaces for workflows that automatically compute material properties greatly simplifies interoperability and cross-verification. We introduce design rules for reusable, code-agnostic, workflow interfaces to compute well-defined material properties, which we implement for eleven quantum engines and use to compute various material properties. Each implementation encodes carefully selected simulation parameters and workflow logic, making the implementer’s expertise of the quantum engine directly available to non-experts. All workflows are made available as open-source and full reproducibility of the workflows is guaranteed through the use of the AiiDA infrastructure.

Long-term confinement of nuclear waste is one of the main challenges faced by the nuclear industry. Fission products such as 90 Sr and 137 Cs, both βemitters known to induce serious health hazards, represent the largest fraction of nuclear waste. Cement is a good candidate to store them, provided it can resist the effects of irradiation over time. Here, we have investigated the effects of βdecay on cement by performing electron irradiation experiments on different samples. We show that H2 production in cement, the main effect of water radiolysis, depends strongly on composition and relative humidity. First-principles calculations indicate that the water-rich interlayer regions with Ca 2+ ions act as electron traps that promote the formation of H2. They also show that holes localize in water-rich regions in low Ca content samples and are then able to participate in H2 production. This work provides new understanding of radiolysis effects in cements.