Build: add support to libxc 6 (#1932)

Author: caic99

CMakeLists.txt

@@ -367,9 +367,12 @@ if(DEFINED Libxc_DIR)
   set(ENABLE_LIBXC ON)
 endif()
 if(ENABLE_LIBXC)
-  find_package(Libxc 5.1.7 REQUIRED HINTS ${Libxc_DIR}/share/cmake/Libxc ${Libxc_DIR}/lib/cmake/Libxc)
+  find_package(Libxc HINTS ${Libxc_DIR}/share/cmake/Libxc ${Libxc_DIR}/lib/cmake/Libxc)
   if(${Libxc_FOUND})
     message(STATUS "Found Libxc: version " ${Libxc_VERSION})
+    if(${Libxc_VERSION} VERSION_LESS 5.1.7)
+      message(FATAL_ERROR "LibXC >= 5.1.7 is required; found ${Libxc_VERSION}")
+    endif()
     target_link_libraries(${ABACUS_BIN_NAME} Libxc::xc)
     include_directories(${Libxc_INCLUDE_DIRS})
     add_compile_definitions(USE_LIBXC)