rmc-discord: reverse Monte Carlo refinement of diffuse scattering and correlated disorder from single crystals

A user-friendly program has been developed to analyze diffuse scattering from single crystals with the reverse Monte Carlo method. The approach allows for refinement of correlated disorder from atomistic supercells with magnetic or structural (occupational and/or displacive) disorder. The program is written in Python and optimized for performance and efficiency. Refinements of two user cases obtained with legacy neutron-scattering data demonstrate the effectiveness of the approach and the developed program. It is shown with bixbyite, a naturally occurring magnetic mineral, that the calculated three-dimensional spin-pair correlations are resolved with finer real-space resolution compared with the pair distribution function calculated directly from the reciprocal-space pattern. With the triangular lattice Ba3Co2O6(CO3)0.7, refinements of occupational and displacive disorder are combined to extract the one-dimensional intra-chain correlations of carbonate molecules that move toward neighboring vacant sites to accommodate strain induced by electrostatic interactions. The program is packaged with a graphical user interface and extensible to serve the needs of single-crystal diffractometer instruments that collect diffuse-scattering data.

Structural and thermodynamic properties for the BaMn(Fe=V)F7 Fluoride glass system by using the Hybrid Reverse Monte Carlo simulation

The Hybrid Reverse Monte Carlo (HRMC) simulation has been widely used as a very useful method for displaying the pair partial distribution functions (PDFs) g(r) eliminating as soon as possible the artificial satellite peaks appear by the RMC simulation. The HRMC is an extension of the RMC algorithm, which introduces an energy penalty term (potential) in the acceptance criteria.The glass retains the structure presented by the liquid at the glass transition temperature Tg, and the thermodynamic properties are influenced by these structural modifications. We are interested in this study to apply the structural parameters g(r), obtained from HRMC simulation, to determine some structural and thermodynamic properties for the BaMn(Fe=V)F7 Fluoride glass.The calculated structural properties such as the running coordination number n(r) were in good agreement with coordination constraint. We suggest also that the structural parameters g(r) is a good tool to determine the thermodynamic properties as the energy of the system.

On the orientational correlations in the supercooled chloride lithium aqueous solution using the hybrid reverse Monte Carlo simulation

Employing the Hybrid Reverse Monte Carlo (HRMC) simulation, we compute, using the obtained three-dimensional configurations, the orientational correlations of water molecules in the supercooled 9.26 molal LiCl aqueous solution. This study aims to add relevant structural properties to those obtained in our latest studies and further support our findings. The Li/Cl pair ions hydration shells and the water molecules distribution studied using the Radial Pair Distribution Functions (RPDF), ([Formula: see text]) and ([Formula: see text]) are further described using the Orientational Pair Correlation Functions (OPCF), [Formula: see text] which describes the probability of a water molecule oriented by the Euler angles [Formula: see text], being located at the position [Formula: see text], with respect to another water molecule oriented [Formula: see text] placed at the origin. The high dimensionality of the orientational correlation functions has not presented a calculation disability, as known with several simulations, in the face of the efficiency of the HRMC and the water–water orientational correlation functions showed the dominant impact of ions on the water molecular dipole orientations within the hydration shells and in the hydrogen bonded molecules network.