The CRYSTAL code, 1976-2020 and beyond, a long story.

CRYSTAL is a periodic ab initio code that uses a Gaussian-type basis set to express crystalline orbitals (i.e., Bloch functions). The use of atom-centered basis functions allows treating 3D (crystals), 2D (slabs), 1D (polymers), and 0D (molecules) systems on the same grounds. In turn, all-electron calculations are inherently permitted along with pseudopotential strategies. A variety of density functionals are implemented, including global and range-separated hybrids of various natures and, as an extreme case, Hartree-Fock (HF). The cost for HF or hybrids is only about 3-5 times higher than when using the local density approximation or the generalized gradient approximation. Symmetry is fully exploited at all steps of the calculation. Many tools are available to modify the structure as given in input and simplify the construction of complicated objects, such as slabs, nanotubes, molecules, and clusters. Many tensorial properties can be evaluated by using a single input keyword: elastic, piezoelectric, photoelastic, dielectric, first and second hyperpolarizabilities, etc. The calculation of infrared and Raman spectra is available, and the intensities are computed analytically. Automated tools are available for the generation of the relevant configurations of solid solutions and/or disordered systems. Three versions of the code exist: serial, parallel, and massive-parallel. In the second one, the most relevant matrices are duplicated on each core, whereas in the third one, the Fock matrix is distributed for diagonalization. All the relevant vectors are dynamically allocated and deallocated after use, making the code very agile. CRYSTAL can be used efficiently on high performance computing machines up to thousands of cores.

Resolving the Amorphous Structure of Lithium Phosphorus Oxynitride (Lipon).

Lithium phosphorus oxynitride, also known as Lipon, solid-state electrolytes are at the center of the search for solid-state Li metal batteries. Key to the performance of Lipon is a combination of high Li content, amorphous character, and the incorporation of N into the structure. Despite the material's importance, our work presents the first study to fully resolve the structure of Lipon using a combination of  ab initio molecular dynamics, density functional theory, neutron scattering, and infrared spectroscopy. The modeled and experimental results have exceptional agreement in both neutron pair distribution function and infrared spectroscopy. Building on this synergy, the structural models show that N forms both bridges between two phosphate units and nonbridging apical N. We further show that as the Li content is increased the ratio of bridging to apical N shifts from being predominantly bridging at Li contents around 2.5:1 Li:P to only apical N at higher Li contents of 3.38:1 Li:P. This crossover from bridging to apical N appears to directly correlate with and explain both the increase in ionic conductivity with the incorporation of N and the ionic conductivity trends found in the literature.

High intensity light pulses to reduce microbial load in fresh cheese.

The present study focused on the utilisation of High Intensity Light Pulses (HILP) treatment to preserve mozzarella cheese. First, the susceptibility of Pseudomonas fluorescens and Enterobacteriaceae to HILP (fluences from 0·39 to 28·0 J/cm2) in a transparent liquid was evaluated (in-vitro tests). Afterwards, the effects on inoculated mozzarella cheese were also assessed. Then untreated (Control) and HILP treated samples were packaged and stored at 10 °C for 2 weeks. Enterobacteriaceae, Pseudomonas spp. and pH were monitored during storage. In a transparent liquid (in-vitro tests) there was a significant microbial inactivation just with 2 s of treatment. On the inoculated cheese a relevant microbial reduction of about 1 log cycle was observed, according to the exposure to the treatments. For Pseudomonas spp. in particular, in the treated samples, the microbiological acceptability limit (106 cfu/g) was never reached after 2 weeks of refrigerated storage. To sum up, the efficacy of this treatment is very interesting because a microbial reduction was observed in treated samples. HILP treatment is able to control the microbial growth and may be considered a promising way to decontaminate the surface of mozzarella cheese.

Katoite under pressure: an ab initio investigation of its structural, elastic and vibrational properties sheds light on the phase transition.

The evolution under pressures up to 65 GPa of structural, elastic and vibrational properties of the katoite hydrogarnet, Ca3Al2(OH)12, is investigated with an ab initio simulation performed at the B3LYP level of theory, by using all-electron basis sets with the Crystal periodic program. The high-symmetry Ia3d phase of katoite, stable under ambient conditions, is shown to be destabilized, as pressure increases, by interactions involving hydrogen atoms and their neighbors which weaken the hydrogen bonding network of the structure. The corresponding thermodynamical instability is revealed by anomalous deviations from regularity of its elastic constants and by numerous imaginary phonon frequencies, up to 50 GPa. Interestingly, as pressure is further increased above 50 GPa, the Ia3d structure is shown to become stable again (all positive phonon frequencies and regular elastic constants). However, present calculations suggest that, above about 15 GPa and up to at least 65 GPa, a phase of I4[combining macron]3d symmetry (a non-centrosymmetric subgroup of Ia3d) becomes more stable than the Ia3d one, being characterized by strengthened hydrogen bonds. At low-pressures (between about 5 GPa and 15 GPa), both phases show some instabilities (more so for I4[combining macron]3d than for Ia3d), thus suggesting either the existence of a third phase or a possible phase transition of second order.

Elasticity of grossular-andradite solid solution: an ab initio investigation.

Grossular and andradite are garnet end-members stable under upper mantle conditions. We perform ab initio simulations to investigate the dependence of the bulk modulus on chemical composition of the grossular-andradite solid solution, Ca3Fe(2-2x)Al(2x)(SiO4)3. All-electron local basis sets of Gaussian-type orbitals and the hybrid B3LYP density functional are used. Our calculations predict a linear modulus-composition trend, in contrast to previous conjectures based on "heterogeneous" experimental measurements. We estimate the largest deviation from linearity to be about 0.5 GPa under ambient conditions, and to progressively reduce to less than 0.2 GPa at pressure P = 20 GPa. The bulk modulus is computed over the whole composition range 0 ≤x≤ 1 following two independent approaches: fitting energy-volume data to an equation-of-state and calculating elastic tensors. Results from the two methods are in perfect agreement, assuring consistency and high numerical accuracy of the adopted algorithms.

Carbon dots from sour whey to develop a novel antimicrobial packaging for fiordilatte cheese.

In this study, monodispersed and quasi-spherical C-Dots with an average size of 7.2 nm were successfully synthesized from sour whey solution by a hydrothermal method (200 °C for 9 h) for fiordilatte cheese packaging. C-Dots (2500 and 5000 mgL-1) were added to the cheese through an alginate-based coating or directly to the cheese brine. No significant changes in TM4 cell viability were observed at concentrations lower than 10,000 mgL-1. Microbiological and sensory properties of cheese coated and uncoated with C-Dots indicate a substantial preserving effect of the C-Dots. The uncoated control fiordilatte exhibited unacceptable levels of microbial proliferation within 3.5 days. Conversely, the coated cheese remained within acceptable limits, effectively doubling its shelf life compared to the control, primarily due to the coating protection rather than the addition of C-Dots. When compared to the control fiordilatte, the addition of C-Dots in the brine at 5000 mgL-1 resulted in an extension of over 10 days in cheese shelf life. Considering the significance of the sustainable approach in C-Dots synthesis and the exceptional use of C-Dots in the food industry, these findings hold great potential in terms of research and industrial applications.

Pomegranate Peel Powder: In Vitro Efficacy and Application to Contaminated Liquid Foods.

In this study the recycling of pomegranate peel powder (PPP) was proposed. In particular, the use of powder loaded in a silk fibroin polymeric matrix to create an active pad was tested. For the sake of comparison, the powder alone was also analysed. Both powder and active pad efficacy was assessed in two different food systems, soymilk (rich in proteins), preliminarily contaminated with Pseudomonas spp. and yeasts, and apple juice (rich in carbohydrates), preliminarily contaminated with Alyciclobacillus acidoterrestris. Three different concentrations of powder alone and powder in the pad were tested (5%, 7.5% and 10% w/v) in both types of beverages. To assess a possible dependence of the efficacy on the powder granulometry, different powder sizes were preliminarily analysed on Pseudomonas spp. and yeasts using an in vitro test. PPP was effective on both Pseudomonas spp. and yeasts. No significant differences appeared among the tested granulometries and therefore in the subsequent tests powder with an average diameter of 250 µm was used. Results recorded with soymilk and apple juice were different. When applied to the soymilk, the activity of PPP in the pad was less effective than that recorded when the powder was directly added to the beverage. With the two highest powder concentrations directly added to food, more than four log cycle reductions in Pseudomonas spp. and yeast cells were recorded, compared to soymilk without any powder. Compared to the control sample, all the soymilk samples either with PPP or with the active pad showed a delayed microbial and fungal growth. When applied to apple juice, both powder and pad were effective at completely inhibiting the proliferation of A. acidoterrestris (<102 CFU/g).

Design principles for NASICON super-ionic conductors.

Na Super Ionic Conductor (NASICON) materials are an important class of solid-state electrolytes owing to their high ionic conductivity and superior chemical and electrochemical stability. In this paper, we combine first-principles calculations, experimental synthesis and testing, and natural language-driven text-mined historical data on NASICON ionic conductivity to achieve clear insights into how chemical composition influences the Na-ion conductivity. These insights, together with a high-throughput first-principles analysis of the compositional space over which NASICONs are expected to be stable, lead to the successful synthesis and electrochemical investigation of several new NASICONs solid-state conductors. Among these, a high ionic conductivity of 1.2 mS cm-1 could be achieved at 25 °C. We find that the ionic conductivity increases with average metal size up to a certain value and that the substitution of PO4 polyanions by SiO4 also enhances the ionic conductivity. While optimal ionic conductivity is found near a Na content of 3 per formula unit, the exact optimum depends on other compositional variables. Surprisingly, the Na content enhances the ionic conductivity mostly through its effect on the activation barrier, rather than through the carrier concentration. These deconvoluted design criteria may provide guidelines for the design of optimized NASICON conductors.

Charge-clustering induced fast ion conduction in 2LiX-GaF3: A strategy for electrolyte design.

2LiX-GaF3 (X = Cl, Br, I) electrolytes offer favorable features for solid-state batteries: mechanical pliability and high conductivities. However, understanding the origin of fast ion transport in 2LiX-GaF3 has been challenging. The ionic conductivity order of 2LiCl-GaF3 (3.20 mS/cm) > 2LiBr-GaF3 (0.84 mS/cm) > 2LiI-GaF3 (0.03 mS/cm) contradicts binary LiCl (10-12 S/cm) < LiBr (10-10 S/cm) < LiI (10-7 S/cm). Using multinuclear 7Li, 71Ga, 19F solid-state nuclear magnetic resonance and density functional theory simulations, we found that Ga(F,X)n polyanions boost Li+-ion transport by weakening Li+-X- interactions via charge clustering. In 2LiBr-GaF3 and 2LiI-GaF3, Ga-X coordination is reduced with decreased F participation, compared to 2LiCl-GaF3. These insights will inform electrolyte design based on charge clustering, applicable to various ion conductors. This strategy could prove effective for producing highly conductive multivalent cation conductors such as Ca2+ and Mg2+, as charge clustering of carboxylates in proteins is found to decrease their binding to Ca2+ and Mg2+.

Calculation of longitudinal polarizability and second hyperpolarizability of polyacetylene with the coupled perturbed Hartree-Fock/Kohn-Sham scheme: where it is shown how finite oligomer chains tend to the infinite periodic polymer.

The longitudinal polarizability, α(xx), and second hyperpolarizability, γ(xxxx), of polyacetylene are evaluated by using the coupled perturbed Hartree-Fock/Kohn-Sham (HF/KS) scheme as implemented in the periodic CRYSTAL code and a split valence type basis set. Four different density functionals, namely local density approximation (LDA) (pure local), Perdew-Becke-Ernzerhof (PBE) (gradient corrected), PBE0, and B3LYP (hybrid), and the Hartree-Fock Hamiltonian are compared. It is shown that very tight computational conditions must be used to obtain well converged results, especially for γ(xxxx), that is, very sensitive to the number of k(->) points in reciprocal space when the band gap is small (as for LDA and PBE), and to the extension of summations of the exact exchange series (HF and hybrids). The band gap in LDA is only 0.01 eV: at least 300 k(->) points are required to obtain well converged total energy and equilibrium geometry, and 1200 for well converged optical properties. Also, the exchange series convergence is related to the band gap. The PBE0 band gap is as small as 1.4 eV and the exchange summation must extend to about 130 Å from the origin cell. Total energy, band gap, equilibrium geometry, polarizability, and second hyperpolarizability of oligomers -(C(2)H(2))(m)-, with m up to 50 (202 atoms), and of the polymer have been compared. It turns out that oligomers of that length provide an extremely poor representation of the infinite chain polarizability and hyperpolarizability when the gap is smaller than 0.2 eV (that is, for LDA and PBE). Huge differences are observed on α(xx) and γ(xxxx) of the polymer when different functionals are used, that is in connection to the well-known density functional theory (DFT) overshoot, reported in the literature about short oligomers: for the infinite model the ratio between LDA (or PBE) and HF becomes even more dramatic (about 500 for α(xx) and 10(10) for γ(xxxx)). On the basis of previous systematic comparisons of results obtained with various approaches including DFT, HF, Moller-Plesset (MP2) and coupled cluster for finite chains, we can argue that, for the infinite chain, the present HF results are the most reliable.

Static and dynamic coupled perturbed Hartree-Fock vibrational (hyper)polarizabilities of polyacetylene calculated by the finite field nuclear relaxation method.

The vibrational contribution to static and dynamic (hyper)polarizability tensors of polyacetylene are theoretically investigated. Calculations were carried out by the finite field nuclear relaxation (FF-NR) method for periodic systems, newly implemented in the CRYSTAL code, using the coupled perturbed Hartree-Fock scheme for the required electronic properties. The effect of the basis set is also explored, being particularly important for the non-periodic direction perpendicular to the polymer plane. Components requiring a finite (static) field in the longitudinal direction for evaluation by the FF-NR method were not evaluated. The extension to that case is currently being pursued. Whereas the effect on polarizabilities is relatively small, in most cases the vibrational hyperpolarizability tensor component is comparable to, or larger than the corresponding static electronic contribution.

Quality Preservation of Ready-to-Eat Prickly Pears by Peels Recycling.

In the current study, prickly pear peel was advantageously recycled to preserve fruit quality. Specifically, the investigated by-products were transformed into powder and then loaded into an alginate-based solution to be applied as coating to peeled prickly pears, to give an example of sustainable minimally processed fruit. For comparison, uncoated fruit, and coated prickly pears without any powder were also prepared. During storage at refrigerated temperature, coated and uncoated samples were tested for weight loss, microbial and fungal proliferation, as well as for sensory quality acceptance. The results were interesting because great differences were found between coated and uncoated fruit, in that coating the fruit delayed weight loss and spoilage, compared to uncoated fruit. Between the simple coating and the coating with peel powder, slight differences were recorded in favor of the peel-enriched coating. In fact, it allowed the promotion of better fruit preservation, and sensory quality. Therefore, prickly pear peels, that represent abundant by-products during prickly pear processing, could be advantageously recycled to preserve fruit quality.

Electric field polarization in conventional density functional theory: from quasilinear to two-dimensional and three-dimensional extended systems.

The large overshoot in (hyper)polarizabilities of quasilinear (1D) chains calculated by applying density functional theory with conventional functionals is investigated for several 2D and 3D extended systems. These systems include arrays of molecular hydrogen chains, as well as 2D coronene-type structures and LiF in 1D, 2D, and 3D. Contrary to a recently proposed model it is found that the overshoot persists in all of these cases. A simple explanation is provided by an analysis of the field-induced charges for molecular hydrogen, which shows an excessive buildup at the chain ends regardless of where the chain is located within the 2D and 3D array.

The superexchange mechanism in crystalline compounds. The case of KMF3(M = Mn, Fe, Co, Ni) perovskites.

The ferromagnetic and antiferromagnetic wavefunctions of four KMF3(M = Mn, Fe, Co and Ni) perovskites have been obtained quantum-mechanically with the CRYSTAL code, by using the Hartree-Fock (HF) Hamiltonian and three flavours of DFT (PBE, B3LYP and PBE0) and anall-electronGaussian type basis set. In the Fe and Co cases, with d6and d7occupation, the Jahn-Teller distortion of the cubic cell is as large as 0.12 Å. Various features of the superexchange interaction energies (SIE), namely additivity, dependence on the M-M distance, on theMFM̂angle, and on the adopted functional, are explored. The contribution to SIE by the Coulomb, exchange and kinetic energy terms is analyzed. It is shown that, when using density functionals, SIE clearly correlates with the amount of exact (Hartree-Fock) exchange in the functional. The effect of SIE on the equilibrium geometry and volume of the unit cell is discussed, and it is shown that the key quantity is the spin polarization of the (closed shell) F ions along the M-F-M path. The effect of thismagneticpressureis evaluated quantitatively for the first time. The superexchange coupling constantJ, evaluated at the HF level and through the Ising model, underestimates the experimental values by about 60%-70%. The more sophisticated Yamaguchi model (that takes into account the contamination of the FM and AFM spin states) does not reduce the discrepancy. The B3LYP hybrid functional overestimates the experiments. These last are bracketed by HF and PBE0. For PBE, the overestimation is huge. Finally, Mulliken population data, charge and spin density maps and density of states are used to illustrate the electronic structure.

Pomegranate Peel Powder as a Food Preservative in Fruit Salad: A Sustainable Approach.

This study aimed to assess the potential of pomegranate peel powder as a natural preservative. Its effects were tested on fruit salad quality decay during refrigerated storage. Nectarine and pineapple, equally portioned in polypropylene containers and covered with fructose syrup, were closed using a screw cap in air, with and without the addition of a by-product peel powder. Specifically, amounts of 2.5% and 5% (w/v) of pomegranate peel powder were put into each container. Both the microbiological and sensory qualities of the fruit salad were monitored during storage at 5 °C for 28 days. The results demonstrated that the fruit salad with the by-products showed lower counts of total mesophilic bacteria, total psychrotrophic microorganisms, yeasts, and lactic acid bacteria compared to the control, thus confirming the recognized antimicrobial properties of pomegranate peel. The other interesting finding of this study is that the addition of the investigated by-product in fruit salad did not worsen the main sensory attributes of fresh-cut fruit. Therefore, these preliminary results suggest that pomegranate peel powder has potential applications as a natural preservative in the fresh-cut food sector.

Improving the Storability of Cod Fish-Burgers According to the Zero-Waste Approach.

This research explored the potential of the zero-waste concept in relation to the storability of fresh food products. In particular, the prickly pear (Opuntia ficus-indica) peel (usually perceived as a by-product) and the pulp were dehydrated, reduced in powder, and used as food additives to slow down the growth of the main spoilage microorganisms of fresh cod fish burgers. The proportion between peel and pulp powder was such as to respect the zero-waste concept. The antibacterial activity of the peel and pulp in proper proportion was first assessed by means of an in vitro test against target microorganisms. Then, the active powder was added at three concentrations (i.e., 2.5 g, 7.5 g, and 12.5 g) to cod fish burgers to assess its effectiveness in slowing down the microbial and sensory quality decay of burgers stored at 4 °C. The results from the in vitro test showed that both the peel and pulp were effective in delaying microbial growth. The subsequent storability test substantially confirmed the in vitro test results. In fact, a significant reduction in growth rate of the main fish spoilage microorganisms (i.e., Pseudomonas spp., psychrotrophic bacteria, and psychrotolerant and heat-labile aerobic bacteria) was observed during 16 days of refrigerated storage. As expected, the antimicrobial effectiveness of powder increased as its concentration increased. Surprisingly, its addition did not affect the sensory quality of fish. Moreover, it was proven that this active powder can improve the fish sensory quality during the storage period.

Synthetic accessibility and stability rules of NASICONs.

In this paper we develop the stability rules for NASICON-structured materials, as an example of compounds with complex bond topology and composition. By first-principles high-throughput computation of 3881 potential NASICON phases, we have developed guiding stability rules of NASICON and validated the ab initio predictive capability through the synthesis of six attempted materials, five of which were successful. A simple two-dimensional descriptor for predicting NASICON stability was extracted with sure independence screening and machine learned ranking, which classifies NASICON phases in terms of their synthetic accessibility. This machine-learned tolerance factor is based on the Na content, elemental radii and electronegativities, and the Madelung energy and can offer reasonable accuracy for separating stable and unstable NASICONs. This work will not only provide tools to understand the synthetic accessibility of NASICON-type materials, but also demonstrates an efficient paradigm for discovering new materials with complicated composition and atomic structure.

Silk Fibroin and Pomegranate By-Products to Develop Sustainable Active Pad for Food Packaging Applications.

In this study, a bio-based polymeric system loaded with fruit by-products was developed. It was based on silk fibroin produced by the silkworm Bombyx mori and pomegranate peel powder, selected as active agent. The weight ratio between fibroin and pomegranate powder was 30:70. Pads also contained 20% w/w of glycerol vs. fibroin to induce water insolubility. Control systems, consisting of only fibroin and glycerol, were produced as reference. Both control and active systems were characterized for structural and morphological characterization (Fourier-transform infrared spectroscopy and optical microscope), antioxidant properties and antimicrobial activity against two foodborne spoilage microorganisms. Results demonstrate that under investigated conditions, an active system was obtained. The pad showed a good water stability, with weight loss of about 28% due to the release of the active agent and not to the fibroin loss. In addition, this edible system has interesting antioxidant and antimicrobial properties. In particular, the pad based on fibroin with pomegranate peel recorded an antioxidant activity of the same order of magnitude of that of vitamin C, which is one of the most well-known antioxidant compounds. As regards the antimicrobial properties, results underlined that pomegranate peel in the pad allowed maintaining microbial concentration around the same initial level (104 CFU/mL) for more than 70 h of monitoring, compared to the control system where viable cell concentration increased very rapidly up to 108 CFU/mL.

Calculation of the first static hyperpolarizability tensor of three-dimensional periodic compounds with a local basis set: A comparison of LDA, PBE, PBE0, B3LYP, and HF results.

The computational scheme for the evaluation of the second-order electric susceptibility tensor in periodic systems, recently implemented in the CRYSTAL code within the coupled perturbed Hartree-Fock (HF) scheme, has been extended to local-density, gradient-corrected, and hybrid density functionals (coupled-perturbed Kohn-Sham) and applied to a set of cubic and hexagonal semiconductors. The method is based on the use of local basis sets and analytical calculation of derivatives. The high-frequency dielectric tensor (epsilon(infinity)) and second-harmonic generation susceptibility (d) have been calculated with hybrid functionals (PBE0 and B3LYP) and the HF approximation. Results are compared with the values of epsilon(infinity) and d obtained from previous plane-wave local density approximation or generalized gradient approximation calculations and from experiment. The agreement is in general good, although comparison with experiment is affected by a certain degree of uncertainty implicit in the experimental techniques.

Sustainable Use of Fruit and Vegetable By-Products to Enhance Food Packaging Performance.

Fruit and vegetable by-products are the most abundant food waste. Industrial processes such as oil, juice, wine or sugar production greatly contribute to this amount. These kinds of residues are generally thrown away in form of leftover and used as feed or composted, but they are a great source of bioactive compounds like polyphenols, vitamins or minerals. The amount of residue with potential utilization after processing has been estimated in millions of tons every year. For this reason, many researchers all around the world are making great efforts to valorize and reuse these valuable resources. Of greatest importance is the by-product potential to enhance the properties of packaging intended for food applications. Therefore, this overview collects the most recent researches dealing with fruit and vegetable by-products used to enhance physical, mechanical, antioxidant and antimicrobial properties of packaging systems. Recent advances on synthetic or bio-based films enriched with by-product components are extensively reviewed, with an emphasis on the role that by-product extracts can play in food packaging materials.