Accurate Hartree-Fock energy of extended systems using large Gaussian basis sets

Calculating highly accurate thermochemical properties of condensed matter via wave function-based approaches (such as e.g. Hartree-Fock or hybrid functionals) has recently attracted much interest. We here present two strategies providing accurate Hartree-Fock energies for solid LiH in a large Gaussian basis set and applying periodic boundary conditions. The total energies were obtained using two different approaches, namely a supercell evaluation of Hartree-Fock exchange using a truncated Coulomb operator and an extrapolation toward the full-range Hartree-Fock limit of a Pad\'e fit to a series of short-range screened Hartree-Fock calculations. These two techniques agreed to significant precision. We also present the Hartree-Fock cohesive energy of LiH (converged to within sub-meV) at the experimental equilibrium volume as well as the Hartree-Fock equilibrium lattice constant and bulk modulus.Comment: 7.5 pages, 2 figures, submitted to Phys. Rev. B; v2: typos removed, References adde

CP2K: An electronic structure and molecular dynamics software package - Quickstep: Efficient and accurate electronic structure calculations

CP2K is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular, and biological systems. It is especially aimed at massively parallel and linear-scaling electronic structure methods and state-of-the-art ab initio molecular dynamics simulations. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern high-performance computing systems. This review revisits the main capabilities of CP2K to perform efficient and accurate electronic structure simulations. The emphasis is put on density functional theory and multiple post–Hartree–Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension

Fifteen species in one: deciphering the Brachionus plicatilis species complex (Rotifera, Monogononta) through DNA taxonomy

Understanding patterns and processes in biological diversity is a critical task given current and rapid environmental change. Such knowledge is even more essential when the taxa under consideration are important ecological and evolutionary models. One of these cases is the monogonont rotifer cryptic species complex Brachionus plicatilis, which is by far the most extensively studied group of rotifers, is widely used in aquaculture, and is known to host a large amount of unresolved diversity. Here we collate a dataset of previously available and newly generated sequences of COI and ITS1 for 1273 isolates of the B. plicatilis complex and apply three approaches in DNA taxonomy (i.e. ABGD, PTP, and GMYC) to identify and provide support for the existence of 15 species within the complex. We used these results to explore phylogenetic signal in morphometric and ecological traits, and to understand correlation among the traits using phylogenetic comparative models. Our results support niche conservatism for some traits (e.g. body length) and phylogenetic plasticity for others (e.g. genome size)

Variable-density Fast-Spin-Echo (FSE) for volumetric inhomogeneous Magnetization Transfer (ihMT) imaging

International audienc

Myeloarchitectonic mapping of cortical gray matter with 3D inhomogeneous magnetization transfer (ihMT)

International audienceAdvances in inhomogeneous magnetization transfer (ihMT) imaging have enabled improved volumetric imaging of gray matter. We performed a cortical surface-based analysis of the ihMT ratio (ihMTR) and the inverse ihMT ratio (ihMTRinv) to investigate the distribution of myelin in cortical gray matter. IhMT MRI, and especially ihMTRinv, displayed regional differences in cortical myelination, in agreement with postmortem studies. These findings support the myelin sensitivity and specificity of ihMTRinv and its use for gray matter characterization

Characterization of the cortical myeloarchitecture with inhomogeneous magnetization transfer imaging (ihMT)

International audienceBackground: Myelin specific imaging techniques to characterize white matter in demyelinating diseases such as multiple sclerosis (MS) have become an area of increasing focus. Gray matter myelination is an important marker of cortical microstructure, and its impairment is relevant in progressive MS. However, its assessment is challenging due to its thin layers. While myelin water imaging and ultra-short TE imaging have not yet been implemented to assess cortical myeloarchitecture, magnetization transfer (MT) shows promise. A recent development of the MT technique, ihMT, has demonstrated greater myelin sensitivity/specificity. Here we implemented a 3D ihMT acquisition and analysis to characterize cortical gray matter myeloarchitecture. Methods: 20 young healthy volunteers were imaged with a 3D ihMTRAGE sequence and quantitative metrics of ihMT (ihMTsat), and dual frequency-offset MT (dual MTsat) were calculated. Cortical surface-based analysis of ihMTsat and dual MTsat were performed and compared. We also compared the cortical ihMTsat map to a cortical surface-based map of T 1-weighted images (T 1 w), defined as a proxy of myelin content. Results: Cortical ihMTsat and dual MTsat maps were in qualitative agreement with previous work and the cortical T 1 w map, showing higher values in primary cortices and lower values in the insula. IhMTsat and dual MTsat were significantly correlated but with important regional differences. The ratio ihMTsat/dual MTsat highlighted higher ihMTsat values in the primary cortices and sulci. Conclusion: ihMTsat, a quantitative metric of ihMT, can be reliably measured in cortical gray matter and shows unique contrast between cortical regions

Myeloarchitectonic mapping of cortical gray matter with 3D inhomogeneous magnetization transfer (ihMT)

International audienceAdvances in inhomogeneous magnetization transfer (ihMT) imaging have enabled improved volumetric imaging of gray matter. We performed a cortical surface-based analysis of the ihMT ratio (ihMTR) and the inverse ihMT ratio (ihMTRinv) to investigate the distribution of myelin in cortical gray matter. IhMT MRI, and especially ihMTRinv, displayed regional differences in cortical myelination, in agreement with postmortem studies. These findings support the myelin sensitivity and specificity of ihMTRinv and its use for gray matter characterization

ISMRM Workshop on Breaking the Barriers of Diffusion MRI

Diffusion MRI (dMRI) is typically performed using single-shot Echo Planar Imaging (ssEPI). However, the long echo-trains in ssEPI result in significant image distortion in the presence of static B0 field inhomogeneties. Several techniques have been proposed for reducing the echo-train length in dMRI in order to reduce image distortions compared to ssEPI. Reduced-Field-of-View (rFOV) imaging has been demonstrated in regions such as the spinal cord [1] and pancreas [2]. Multi-shot EPI (msEPI) is based on an interleaved segmented k-space acquisition that enables full FOV dMRI with reduced distortion (upon correction of inter-shot phase inconsistencies) [3]. Both rFOV and msEPI have been shown to provide high quality diffusion weighted images. However, their ability to provide accurate quantitative diffusion measures has not been fully characterized. In this study we extend the work from Banerjee et al [4] by conducting controlled experiments in two recently proposed quantitative diffusion phantoms to compare the apparent diffusion coefficient (ADC) measured from three diffusion sequences: ssEPI, rFOV and msEPI.Ministerio de Ciencia, Innovación y Universidades (TEC 2013-44194P and TEC 2014-57428