By analyzing structural and electronic properties of more than a hundred predicted hydrogen-based superconductors, we determine that the capacity of creating an electronic bonding network between localized units is key to enhance the critical temperature in hydrogen-based superconductors. We define a magnitude named as the networking value, which correlates with the predicted critical temperature better than any other descriptor analyzed thus far. By classifying the studied compounds according to their bonding nature, we observe that such correlation is bonding-type independent, showing a broad scope and generality. Furthermore, combining the networking value with the hydrogen fraction in the system and the hydrogen contribution to the density of states at the Fermi level, we can predict the critical temperature of hydrogen-based compounds with an accuracy of about 60 K. Such correlation is useful to screen new superconducting compounds and offers a deeper understating of the chemical and physical properties of hydrogen-based superconductors, while setting clear paths for chemically engineering their critical temperatures.
It has become recently clear that chemical bonding under pressure is still lacking guiding principles for understanding the way electrons reorganize when their volume is constrained. As an example, it has recently been shown that simple metals can become insulators (aka electrides) when submitted to high enough pressures. This has lead to the general believe that "a fundamental yet empirically useful understanding of how pressure alters the chemistry of the elements is lacking" (Hemley, 2010). We will show that a simple 1-dimensional double well potential with non-interacting electrons and its Electron Localization Function (ELF) mimic the sequence of chemical bonding undergone by atomic solids under pressure. First transforming into metals (predicted already in 1935) and finally to an electride form. This simple model provides a fast and visual framework for transformations in the electronic structure in the high-pressure regime in terms of two chemically sound parameters related to external potential and confinement. We are interested in understanding the role the Pauli principle plays on the localization/delocalization of non-interacting confined electrons. I. INTRODUCTION Confinement can dramatically change the microscopic structure of electronic systems because it increases the electrostatic repulsion between electrons and also makes Pauli repulsion more relevant.[1, 2] This leads to radically new materials with exotic and unexpected properties.[3] [4] As a recent example, superconductivity has shown to become common even in small and well known molecular solids such as H 2 S.[5]
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