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Isomers of (NaCl)n(H2O)2n clusters, with n = 1, 2 and 4, were investigated using an implementation of the simulated annealing method that imposes a virtual confinement on each isomer to stay within a sphere with an arbitrary radius. By using several confinement radii, we reported 2, 56 and 38 isomers for n = 1, 2 and 4, respectively. For n = 1, the CCSD(T)/aug-cc-pVTZ method was used as a reference by optimizing the corresponding isomers. These results were contrasted with those obtained by the MP2 method and eight exchange–correlation functionals: PBE, PBE0, B3LYP, PBE-D3, PBE0-D3, B3LYP-D3, LC-̉PBE and M06-2X. From this analysis we conclude that the M06-2X method gives reliable results and then, isomers with n = 2 and 4 were analyzed with this exchange–correlation functional. From the analysis of these two systems, the resulting isomers with the lowest energy showed cuboid structures and no breaking bond was present for NaCl molecules. Thus, in the nucleation process of the NaCl dihydrate our results suggest that the Na–Cl bond is present. Besides, bond length and electron density evaluated at bond critical points for the biggest system delivered values close to those found in the crystal structure. [ABSTRACT FROM AUTHOR]

Using a grid-based method to search the critical points in electron density, we show how to accelerate such a method with graphics processing units (GPUs). When the GPU implementation is contrasted with that used on central processing units (CPUs), we found a large difference between the time elapsed by both implementations: the smallest time is observed when GPUs are used. We tested two GPUs, one related with video games and other used for highperformance computing (HPC). By the side of the CPUs, two processors were tested, one used in common personal computers and other used for HPC, both of last generation. Although our parallel algorithm scales quite well on CPUs, the same implementation on GPUs runs around 10× faster than 16 CPUs, with any of the tested GPUs and CPUs. We have found what one GPU dedicated for video games can be used without any problem for our application, delivering a remarkable performance, in fact; this GPU competes against one HPC GPU, in particular when single-precision is used. [ABSTRACT FROM AUTHOR]

For the first time, the electron density of the H2+ molecule is analyzed when this system is confined by spheroidal walls with an infinite potential. Typically, this system is studied to obtain information of the total energy and its components or to gain insight of some expected values when such a system is squeezed by this kind of confinement. However, this is the first report where the electron density and its derivatives, under the quantum theory of atoms in molecules (QTAIM), are analyzed to study the chemical bond involved with this molecule. This confinement induces an unexpected behavior of the chemical bond and gives an idea about atomic interactions under high pressures, where the QTAIM approach indicates that the chemical bond disappears. For strong confinements, there is a significant contribution of the electron kinetic energy and the nuclear‐electron energy contribution can be neglected. Under this situation, the confined H2+ system is another example where the notion of the topological atom given by the QTAIM is no longer suitable. [ABSTRACT FROM AUTHOR]

The analysis of scalar and vector fields in quantum chemistry is an essential task for the computational chemistry community, where such quantities must be evaluated rapidly to perform a particular study. For example, the atoms in molecules approach proposed by Bader has become popular; however, this method demands significant computational resources to compute the involved tasks in short times. In this article, we discuss the importance of graphics processing units (GPU) to analyze electron density, and related fields, implementing several scalar, and vector fields within the graphics processing units for atoms and molecules (GPUAM) code developed by a group of the Universidad Autónoma Metropolitana in México City. With this application, the quantum chemistry community can perform demanding computational tasks on a desktop, where CPUs and GPUs are used to their maximum capabilities. The performance of GPUAM is tested in several systems and over different GPUs, where a GPU installed in a workstation converts it to a robust high‐performance computing system. The Graphics Processing Units for Atoms in Molecules (GPUAM) project is benchmarked in several systems and over different GPUs, where a GPU installed in a workstation converts it to a robust high‐performance computing system. Developed at the Universidad Autónoma Metropolitana in México City, GPUAM can evaluate electron density, or related scalar or vector quantum chemistry fields, using CPUs and GPUs over desktops, or high‐performance computing hardware. [ABSTRACT FROM AUTHOR]