title: Ten new predicted covalent organic frameworks with strong optical response in the visible and near infrared.
abstract: We use density functional theory to predict and evaluate 10 novel covalent organic frameworks (COFs), labeled (X4Y)(BDC)3, (X = C/Si; Y = C, Si, Ge, Sn, and Pb), with topology based on metal organic framework isoreticular metal-organic framework (IRMOF-1), but with new elements substituted for the corner atoms. We show that these new materials are stable structures using frequency calculations. For two structures, (C4C and Si4C) molecular dynamics simulations were performed to demonstrate stability of the systems up to 600 K for 10 ps. This demonstrates the remarkable stability of these systems, some of which may be experimentally accessible. For the C4C material, we also explored the stability of isolated corners and linkers and vacuum and started to build the structure from these pieces. We discuss the equilibrium lattice parameters, formation enthalpies, electronic structures, chemical bonding, and mechanical and optical properties. The predicted bulk moduli of these COFs range from 18.9 to 23.9 GPa, larger than that of IRMOF-1 (ca. 15.4 GPa), and larger than many existing 3D COF materials. The band gaps range from 1.5 to 2.1 eV, corresponding to 600-830 nm wavelength (orange through near infrared). The negative values of the formation enthalpy suggest that they are stable and should be experimentally accessible under suitable conditions. Seven materials distort the crystal structure to a lower space group symmetry Fm-3, while three materials maintain the original Fm-3m space group symmetry. All of the new materials are highly luminescent. We hope that this work will inspire efforts for experimental synthesis of these new materials.
authors.affiliation: Bremen Center for Computational Materials Science, University of Bremen, Am Falturm 1, 28359 Bremen, Germany.
authors.forename: Li-Ming
authors.initials: LM
authors.lastname: Yang
authors.affiliation: Department of Physics, University of Minnesota, 116 Church St., SE, Minneapolis, Minnesota 55416, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Dornfeld
authors.affiliation: Department of Physics, University of Minnesota, 116 Church St., SE, Minneapolis, Minnesota 55416, USA.
authors.forename: Pik-Mai
authors.initials: PM
authors.lastname: Hui
authors.affiliation: Bremen Center for Computational Materials Science, University of Bremen, Am Falturm 1, 28359 Bremen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Frauenheim
authors.affiliation: Department of Physics, University of Minnesota, 116 Church St., SE, Minneapolis, Minnesota 55416, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Ganz