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

Elissaios Stavrou; M Riad Manaa; Joseph M Zaug; I-Feng W Kuo; Philip F Pagoria; Bora Kalkan; Jonathan C Crowhurst; Michael R Armstrong

doi:10.1063/1.4932683

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

J Chem Phys. 2015 Oct 14;143(14):144506. doi: 10.1063/1.4932683.

Authors

Elissaios Stavrou¹, M Riad Manaa¹, Joseph M Zaug¹, I-Feng W Kuo¹, Philip F Pagoria¹, Bora Kalkan², Jonathan C Crowhurst¹, Michael R Armstrong¹

Affiliations

¹ Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
² Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720, USA.

PMID: 26472388
DOI: 10.1063/1.4932683

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.