title: The high pressure structure and equation of state of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) up to 20 GPa: X-ray diffraction measurements and first principles molecular dynamics simulations.
abstract: Recent theoretical studies of 2,6-diamino-3,5-dinitropyrazine-1-oxide (C4H4N6O5 Lawrence Livermore Molecule No. 105, LLM-105) report unreacted high pressure equations of state that include several structural phase transitions, between 8 and 50 GPa, while one published experimental study reports equation of state (EOS) data up to a pressure of 6 GPa with no observed transition. Here we report the results of a synchrotron-based X-ray diffraction study and also ambient temperature isobaric-isothermal atomistic molecular dynamics simulations of LLM-105 up to 20 GPa. We find that the ambient pressure phase remains stable up to 20 GPa; there is no indication of a pressure induced phase transition. We do find a prominent decrease in b-axis compressibility starting at approximately 13 GPa and attribute the stiffening to a critical length where inter-sheet distance becomes similar to the intermolecular distance within individual sheets. The ambient temperature isothermal equation of state was determined through refinements of measured X-ray diffraction patterns. The pressure-volume data were fit using various EOS models to yield bulk moduli with corresponding pressure derivatives. We find very good agreement between the experimental and theoretically derived EOS.
authors.affiliation: Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
authors.forename: Elissaios
authors.initials: E
authors.lastname: Stavrou
authors.affiliation: Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
authors.forename: M
authors.initials: M
authors.lastname: Riad Manaa
authors.affiliation: Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Zaug
authors.affiliation: Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
authors.forename: I-Feng W
authors.initials: IF
authors.lastname: Kuo
authors.affiliation: Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
authors.forename: Philip F
authors.initials: PF
authors.lastname: Pagoria
authors.affiliation: Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720, USA.
authors.forename: Bora
authors.initials: B
authors.lastname: Kalkan
authors.affiliation: Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Crowhurst
authors.affiliation: Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Armstrong