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The LaTiO3 perovskite (where Ti is in a d1 state) is investigated by using an all electron Gaussian basis and many functionals, ranging from pure GGA (PBE), to hybrids (full range, B3LYP and PBE0, and range separated, HSE06) to Hartree Fock. Recently, Varignon et al. (Phys. Rev. Res 1, 033131, 2019), showed that, when GGA+U or HSE06 are used, a metallic solution and fractional occupancy of the t2g subshell are obtained. Here, it is shown that when a full range hybrid functional is used, an integer occupancy is obtained, as suggested by the Jahn-Teller theorem. When the exact exchange percentage varies from 0 to 100, the system is insulating when it exceeds 20. By reducing progressively the symmetry from cubic down to orthorhombic, the relative importance of the Jahn-Teller deformation and of the rotation of the octahedra is explored. [ABSTRACT FROM AUTHOR]

We present a detailed density functional theory study of beryllium nitride Be3N2 in several periodic arrangements ranging from the 3D bulk, the 2D slab model to the 1D (n,0) zigzag single walled nanotubes using B3LYP hybrid functional and Gaussian-type basis sets. IR and Raman spectra are computed through a coupled-perturbed KS/HF scheme permitting identification of all arrangements. For (n,0) single-walled zigzag beryllium nitride nanotubes, the cohesive, rolling and relaxation energies, band-gaps, equilibrium geometries, polarizabilities and vibrational spectra are established where the trend towards the hexagonal monolayer (h- Be3N2) is explored. Their IR spectrum presents two frequency ranges (500–650 cm−1) and (1350–1500 cm−1) that tend towards the optical vibrational modes of the 2D h- Be3N2 layer. Four sets of active bands are observed in their Raman spectrum. The first set contains two Raman modes with vanishing wave numbers when the nanotube radius increases and found to be connected to the elastic constants C12 and C66 of the h- Be3N2 single layer. The second (300–700 cm−1) and fourth (1200–1600 cm−1) modes are intrinsic nanotube active modes that result from the periodic boundary condition along the circumference. The third set (800–1000 cm−1) contains two phonon modes A'1 and E'1 that tend to the Raman active mode E2g of the 2D monolayer. This theoretical contribution should motivate new experimental works dealing with the design and optimization of low-dimensional beryllium nitrides. [ABSTRACT FROM AUTHOR]

The structure and cohesive energy of crystalline urea are investigated at the ab initio level of calculation by adopting Hartree-Fock (HF) and Density Functional Theory (DFT) methods in solid-state chemistry. Results show that DFT methods underestimate cohesive energies due to the lack of dispersion interactions and this translates to overestimated unit cell volumes.

A study of the structure of an azamacrocycle, C(sub 26)H(sub 18)N(sub 6) using Hartree-Fock, local density and gradient corrected density functional calculation is presented. The results show that two approximately planar elliptical structures with C2 or C1 symmetry are found to be nearly degenerate and this difference is mainly due to electrostatic interactions.

A general methodology has been devised and implemented into the solid-state ab initio quantummechanical CRYSTAL program for studying the evolution under geophysical pressure of the elastic anisotropy of crystalline materials. This scheme, which fully exploits both translational and point symmetry of the crystal, is developed within the formal frame of one-electron Hamiltonians and atom-centered basis functions. Six silicate garnet end-members, among the most important rockforming minerals of the Earth's mantle, are considered, whose elastic anisotropy is fully characterized under high hydrostatic compressions, up to 60 GPa. The pressure dependence of azimuthal anisotropy and shear-wave birefringence of seismic wave velocities for these minerals are accurately simulated and compared with available single-crystal measurements. [ABSTRACT FROM AUTHOR]

Aims: Implant-associated infections arise from the formation of bacterial biofilms, which are difficult to be treated with conventional antibiotics. Therefore, there is a need for new implant functionalizations, which inhibit biofilm formation. The aim of the present study was to characterize the effect of synthetic peptides to assess their applicability for this purpose. Methods and Results: Two synthetic anti-endotoxin peptides, Pep19-2.5 and Pep19-4LF (Aspidasept I and II) were tested against both Gram-positive (Staphylococcus aureus and Streptococcus oralis) and Gram-negative (Pseudomonas aeruginosa and Aggregatibacter actinomycetemcomitans) bacteria associated with implant infections. Their activity was evaluated against different states of biofilm formation on the implant material titanium using CFU, live/dead fluorescence staining and confocal microscopy. Both peptides inhibited planktonic bacteria growth, impacted initial bacterial adhesion, reduced biofilm volume and increased the proportion of dead cells. Additionally, cytotoxicity analyses showed that neither peptide harmed human gingival fibroblasts nor osteoblasts at lower concentrations. Conclusion: A concentration-dependent antibacterial activity of both peptides against biofilms of four clinically relevant bacteria could be demonstrated. Significance and Impact of the Study: The results of this study serve as a promising basis for the improvement of these peptides in order to finally achieve a peptide-equipped antibacterial implant surface. [ABSTRACT FROM AUTHOR]

A global search for possible LiF cluster structures is performed up to (LiF)8. The method is based on simulated annealing, where all the energies are evaluated on the ab initio level. In addition, the threshold algorithm is employed to determine the energy barriers for the transitions among these structures, for the cluster (LiF)4, again on the ab initio level, and the corresponding tree graph is obtained. [ABSTRACT FROM AUTHOR]

The development of novel and innovative biomaterials and biomedical devices like medical implants is a sophisticated task that requires expertise ranging from physicians over engineers and natural scientists to regulatory officers for clinical translation to be most efficient. This short communication should highlight the specific requirements and perspectives of the different disciplines and conclude on the importance of interdisciplinary training for early-stage researchers. For this purpose, experts for clinical practice, material development, biological testing and medical device approval with profound experience in interdisciplinary research summarized and discussed current literature and knowledge. Multiple interactions right from the start of the design phase until the medical device approval could clearly be identified. As not all relevant study programs already include interdisciplinary training, implementing structured interdisciplinary doctoral programs is advised to accelerate innovative biomedical implant development.

The LaTiO3 perovskite (where Ti is in a d1 state) is investigated by using an all electron Gaussian basis and many functionals, ranging from pure GGA (PBE), to hybrids (full range, B3LYP and PBE0, and range separated, HSE06) to Hartree Fock. Recently, Varignon et al. (Phys. Rev. Res 1, 033131, 2019), showed that, when GGA+U or HSE06 are used, a metallic solution and fractional occupancy of the t2g subshell are obtained. Here, it is shown that when a full range hybrid functional is used, an integer occupancy is obtained, as suggested by the Jahn-Teller theorem. When the exact exchange percentage varies from 0 to 100, the system is insulating when it exceeds 20. By reducing progressively the symmetry from cubic down to orthorhombic, the relative importance of the Jahn-Teller deformation and of the rotation of the octahedra is explored. [ABSTRACT FROM AUTHOR]

To prevent implant-associated infections, surface modifications need to be developed that prevent bacterial colonisation and biofilm formation. In the present study, titanium surfaces were processed by nanosecond-pulsed laser ablation to generate a variety of different structures (anatase, rutile, Osteon, as well as Osteon additionally coated with silver and clove nanoparticles). Analysis of adhesion and biofilm formation of the oral pioneer bacterium Streptococcus oralis could demonstrate antibacterial properties of anatase surfaces. For clinical translation, the effect should be enhanced by further adaption and combined with the osseointegrative Osteon structure

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A quantum mechanical molecular mechanics (QM/MM) implementation for periodic systems is reported. This is done for the case of molecules and for systems with two and three-dimensional periodicity, which is suitable to model electrolytes in contact with electrodes. Tests on different water-containing systems, ranging from the water dimer up to liquid water indicate the correctness of the scheme. Furthermore, molecular dynamics simulations are performed, as a possible direction to study realistic systems. A QM/MM scheme is implemented for periodic systems, employing a subtractive scheme and mechanical embedding. The implementation is based on the MM code GULP and the QM code CRYSTAL. As an example, radial pair distribution functions of water are studied on the MM and QM/MM level. [ABSTRACT FROM AUTHOR]

Abstract: An ab initio DFT-based study of the electronic band structure and elastic properties of the new lithium ion conductors Li2B3O4F3 and Li2B6O9F2 has been performed. The hybrid functional B3LYP was employed with the CRYSTAL code, and the local density approximation (LDA) with the VASP code. Starting from the experimentally determined structures, both crystals were computationally optimized. The relaxed structures were found to be very close to the initial, experimental, ones. The band structure shows wide band gaps E g, near 9–10eV (B3LYP) or 6–7eV (LDA), depending on the level of theory applied. The top valence bands of both crystals mainly derive from oxygen and fluorine, and the bottom conduction bands are mainly associated with boron and oxygen. An analysis of the elastic properties of the two compounds has been done, and all coefficients of the elastic stiffness tensor c ij and the bulk modulus B are calculated. The interatomic distances, Mulliken charges and overlap populations are discussed from the viewpoint of lithium ion conductivity. [Copyright &y& Elsevier]

Metal-pernitride compounds belong to a class of chemical systems in which both the complex ions and the non-bonding electrons may play roles in the formation of their modified crystalline structures. To investigate this issue, the energy landscapes of pernitrides of metals with different maximum valence (M=Ca, Sr, Ba, La, and Ti) were globally explored on the ab initio level at standard and high pressures, thereby yielding possible (meta)stable modifications in these systems together with information on how the landscape changed as function of the valence of the metal cation. For all of the systems in which no compounds had been synthesized so far, we predicted the existence of kinetically stable modifications that should, in principle, be experimentally accessible. In particular, TiN2 should crystallize in a new structure type, TiN2-I. [ABSTRACT FROM AUTHOR]

We perform a global search for possible structures of bulk lithium, where we employ simulated annealing with ab initio energies in all steps. We find the A 15 structure as a different promising local minimum at ambient pressure. Its energy is competitive with the already known structures, thus making it an interesting target for synthesis. [ABSTRACT FROM AUTHOR]

An important issue in modern solid state chemistry is the development of a general methodology to predict the possible (meta)-stable modifications of a solid. This requires the global exploration of the energy landscape of the chemical system, since each stable phase corresponds to a locally ergodic region of the landscape. The global search in the lead sulfide system has been performed with simulated annealing on the ab initio level, while zinc oxide was studied with an empirical potential using simulated annealing, both at standard and elevated pressure (up to 100 GPa). The local optimization of the modifications found in the PbS system was performed using various density functionals. Next, the energy E(V ) and enthalpy H(p) as function of volume and pressure, respectively, were computed for these modifications and their electronic structure was analyzed. The structures found for ZnO were locally optimized on ab initio level (DFT and Hartree-Fock). In both systems the structures found were in good agreement with the experiment. Furthermore, we employed the threshold algorithm to explore the barrier structure of the landscape of ZnO as function of the number of formula units in the simulation cell. Based on the barrier and minima information 2-D models of the energy landscape were constructed. [ABSTRACT FROM AUTHOR]

As lead sulfide is an important semiconductor, it is of great interest to identify possible (meta)stable modifications, both at standard and elevated pressures. To predict such structures, global optimizations on the energy landscape of PbS were performed for several pressures, using simulated annealing followed by local optimization of the candidates found. In order to be able to take the effect of the nonbonding valence electrons of Pb into account, ab initio energies were employed for both the global and local optimization. Besides the experimentally known modifications (NaCl structure type at standard pressure and the CsCl structure type at high pressure), several additional promising structures, which might be accessible synthetically, were found; exhibiting, e.g., the TlI type (Cmcm), the FeB type (Pnma), and the α-GeTe type (R3m). [ABSTRACT FROM AUTHOR]

The performance of six different density functionals (LDA, PBE, PBESOL, B3LYP, PBE0, and WC1LYP) in describing the infrared spectrum of forsterite, a crystalline periodic system with orthorhombic unit cell (28 atoms in the primitive cell, Pbmn space group), is investigated by using the periodic ab initio CRYSTAL09 code and an all-electron Gaussian-type basis set. The transverse optical (TO) branches of the 35 IR active modes are evaluated at the equilibrium geometry together with the oscillator strengths and the high-frequency dielectric tensor ϵ. These quantities are essential to compute the dielectric function ϵ(ν), and then the reflectance spectrum R(ν), which is compared with experiment. It turns out that hybrid functionals perform better than LDA and GGA, in general; that B3LYP overperforms WC1LYP and, in turn, PBE0; that PBESOL is better than PBE; that LDA is the worst performing functional among the six under study. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011 [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure and related physical properties of crystalline ammonium sulfate, (NH4)2SO4, have been studied using the first principles code CRYSTAL06 at the B3LYP level of theory. The title compound has been found to possess one stable and three metastable configurations, all within the polar space group Pna21 (no. 33). Two of the metastable polymorphs are newly predicted and have not yet been observed experimentally. The different configurations show considerably varying magnitudes of the spontaneous polarization P s . All coefficients of the elastic stiffness tensor, c kl , and elasto-electrical tensor, e ki have been calculated for the first time and have been found to agree satisfactorily with experimental data, as far as available. [Copyright &y& Elsevier]