if(PKG_OPT)
    set(OPT_SOURCES_DIR ${LAMMPS_SOURCE_DIR}/OPT)
    set(OPT_SOURCES)
    set_property(GLOBAL PROPERTY "OPT_SOURCES" "${OPT_SOURCES}")

    # detects styles which have OPT version
    RegisterStylesExt(${OPT_SOURCES_DIR} opt OPT_SOURCES)

    get_property(OPT_SOURCES GLOBAL PROPERTY OPT_SOURCES)

    list(APPEND LIB_SOURCES ${OPT_SOURCES})
    include_directories(${OPT_SOURCES_DIR})
endif()