Energy and Electronic Properties of Nanostructures Based on the CL-20 Framework with the Replacement of the Carbon Atoms by Silicon and Germanium: A Density Functional Theory Study

Margarita A Gimaldinova; Mikhail M Maslov; Konstantin P Katin

doi:10.3390/ma15196577

Energy and Electronic Properties of Nanostructures Based on the CL-20 Framework with the Replacement of the Carbon Atoms by Silicon and Germanium: A Density Functional Theory Study

Materials (Basel). 2022 Sep 22;15(19):6577. doi: 10.3390/ma15196577.

Authors

Margarita A Gimaldinova¹, Mikhail M Maslov^{1

2}, Konstantin P Katin^{1

2}

Affiliations

¹ Nanoengineering in Electronics, Spintronics and Photonics Institute, National Research Nuclear University "MEPhI", Kashirskoe Shosse 31, 115409 Moscow, Russia.
² Laboratory of Computational Design of Nanostructures, Nanodevices, and Nanotechnologies, Research Institute for the Development of Scientific and Educational Potential of Youth, Aviatorov Str. 14/55, 119620 Moscow, Russia.

Abstract

We consider Si_nCL-20 and Ge_nCL-20 systems with carbon atoms replaced by silicon/germanium atoms and their dimers. The physicochemical properties of the silicon/germanium analogs of the high-energy molecule CL-20 and its dimers were determined and studied using density functional theory with the B3LYP/6-311G(d,p) level of theory. It was found that the structure and geometry of Si_nCL-20/Ge_nCL-20 molecules change dramatically with the appearance of Si-/Ge-atoms. The main difference between silicon- or germanium-substituted Si_nCL-20/Ge_nCL-20 molecules and the pure CL-20 molecule is that the NO₂ functional groups make a significant rotation relative to the starting position in the classical molecule, and the effective diameter of the frame of the systems increases with the addition of Si-/Ge-atoms. Thus, the effective framework diameter of a pure CL-20 molecule is 3.208 Å, while the effective diameter of a fully silicon-substituted Si₆CL-20 molecule is 4.125 Å, and this parameter for a fully germanium-substituted Ge₆CL-20 molecule is 4.357 Å. The addition of silicon/germanium atoms to the system leads to a decrease in the binding energy. In detail, the binding energies for CL-20/Si₆CL-20/Ge₆CL-20 molecules are 4.026, 3.699, 3.426 eV/atom, respectively. However, it has been established that the framework maintains stability, with an increase in the number of substituting silicon or germanium atoms. In addition, we designed homodesmotic reactions for the CL-20 molecule and its substituted derivatives Si₆CL-20/Ge₆CL-20, and then determined the strain energy to find out in which case more energy would be released when the framework breaks. Further, we also studied the electronic properties of systems based on CL-20 molecules. It was found that the addition of germanium or silicon atoms instead of carbon leads to a decrease in the size of the HOMO-LUMO gap. Thus, the HOMO-LUMO gaps of the CL-20/Si₆CL-20/Ge₆CL-20 molecules are 5.693, 5.339, and 5.427 eV, respectively. A similar dependence is also observed for CL-20 dimers. So, in this work, we have described in detail the dependence of the physicochemical parameters of CL-20 molecules and their dimers on the types of atoms upon substitution.

Keywords: CL-20; chemical reactivity; covalent dimers; density functional theory; high-energy molecules; strain energy.

Grants and funding

Priority 2030/NRNU MEPhI program Priority 2030