A Comparative Density Functional Theory and Density Functional Tight Binding Study of Phases of Nitrogen Including a High Energy Density Material N8

Nicholas Capel,Sergei Manzhos,Devang Bharania

doi:10.3390/computation3040574

Abstract

We present a comparative dispersion-corrected Density Functional Theory (DFT) and Density Functional Tight Binding (DFTB-D) study of several phases of nitrogen, including the well-known alpha, beta, and gamma phases as well as recently discovered highly energetic phases: covalently bound cubic gauche (cg) nitrogen and molecular (vdW-bound) N8 crystals. Among several tested parametrizations of N–N interactions for DFTB, we identify only one that is suitable for modeling of all these phases. This work therefore establishes the applicability of DFTB-D to studies of phases, including highly metastable phases, of nitrogen, which will be of great use for modelling of dynamics of reactions involving these phases, which may not be practical with DFT due to large required space and time scales. We also derive a dispersion-corrected DFT (DFT-D) setup (atom-centered basis parameters and Grimme dispersion parameters) tuned for accurate description simultaneously of several nitrogen allotropes including covalently and vdW-bound crystals and including high-energy phases.

Highlights

The development of new high energy density materials (HEDM) is important for a range of applications including explosives and chemical energy storage [1]
Density Functional Theory (DFT) simulations were performed with the SIESTA code [35] using the PBE exchange-correlation functional [36]
It is important to understand if existing parameterizations of Density Functional Tight Binding (DFTB) are suitable for modeling of allotropes of nitrogen, including high-energy phases

Summary

Introduction

The development of new high energy density materials (HEDM) is important for a range of applications including explosives and chemical energy storage [1] Desired properties for such materials include high energy density and stability in common environments as well as under stimuli. Most effective molecular HEDM contain nitrogen- and oxygen-containing heterocycles and/or NOx moieties [10]. The decomposition of such molecules usually leads to the release of COx, NOx and cyanogen molecules which are toxic or environmentally damaging [2,3,4,5,6,7,8,9]

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Conclusion