diff --git a/src/external/libGapIntegrals/CMakeLists.txt b/src/external/libGapIntegrals/CMakeLists.txt
new file mode 100644
index 00000000..ea67b173
--- /dev/null
+++ b/src/external/libGapIntegrals/CMakeLists.txt
@@ -0,0 +1,71 @@
+# - libGapIntegrals library ---------------------------------------------------
+
+#--- generate necessary dictionaries ------------------------------------------
+set(MUSRFIT_INC ${CMAKE_SOURCE_DIR}/src/include)
+set(BMW_TOOLS_INC ${CMAKE_SOURCE_DIR}/src/external/BMWtools)
+
+root_generate_dictionary(
+  TGapIntegralsDict 
+  -I${FFTW3_INCLUDE_DIR} 
+  -I${MUSRFIT_INC}
+  -I${BMW_TOOLS_INC}
+  TGapIntegrals.h
+  LINKDEF TGapIntegralsLinkDef.h
+)
+
+#--- create pkg-config info ---------------------------------------------------
+#[==[ //as35 for now do not create a pkgconfig file
+set(prefix "${CMAKE_INSTALL_PREFIX}")   
+set(exec_prefix "\$\{prefix\}")
+set(libdir "\$\{exec_prefix\}/lib")
+set(includedir "\$\{prefix\}/include")   
+set(GAP_INTEGRALS_VERSION "1.0.0")
+set(GAP_INTEGRALS_LIBRARY_NAME "GapIntegrals")
+configure_file("GapIntegrals.pc.in" "GapIntegrals.pc" @ONLY)
+#]==]
+
+#--- lib creation -------------------------------------------------------------
+add_library(GapIntegrals SHARED
+  TGapIntegrals.cpp
+  TGapIntegralsDict.cxx
+)
+#--- make sure that the include directory is found ----------------------------
+target_include_directories(
+  GapIntegrals BEFORE PRIVATE 
+    $<BUILD_INTERFACE:${FFTW3_INCLUDE_DIR}> 
+    $<BUILD_INTERFACE:${MUSRFIT_INC}>
+    $<BUILD_INTERFACE:${BMW_TOOLS_INC}>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+)
+
+#--- add library dependencies -------------------------------------------------
+target_link_libraries(GapIntegrals 
+  ${GSL_LIBRARIES} ${FFTW3F_LIBRARY} ${ROOT_LIBRARIES} PUserFcnBase cuba BMWtools
+)
+
+#--- install LFRelaxation solib -----------------------------------------------
+install(TARGETS GapIntegrals DESTINATION lib)
+
+#--- install root pcm's and rootmaps ------------------------------------------
+install(
+  FILES ${CMAKE_CURRENT_BINARY_DIR}/libTGapIntegralsDict_rdict.pcm
+        ${CMAKE_CURRENT_BINARY_DIR}/libTGapIntegralsDict.rootmap
+  DESTINATION lib
+)
+
+#--- install GapIntegrals header ----------------------------------------------
+install(
+  FILES 
+    TGapIntegrals.h
+  DESTINATION 
+    include
+)
+
+#--- install pkg-config info --------------------------------------------------
+#[==[ //as35 for now do not install a pkgconfig file
+install(
+  FILES ${CMAKE_CURRENT_BINARY_DIR}/GapIntegrals.pc
+  DESTINATION lib/pkgconfig
+)
+#]==]
+