diff -rupN kalzium-16.08.3/CMakeLists.txt kalzium-16.08.3-new/CMakeLists.txt
--- kalzium-16.08.3/CMakeLists.txt	2016-12-22 11:12:40.135985025 +0100
+++ kalzium-16.08.3-new/CMakeLists.txt	2016-12-22 11:12:50.983986130 +0100
@@ -35,7 +35,7 @@ kde4_no_enable_final(kalzium)
 
 include(KalziumConfigureChecks.cmake)
 
-if (OPENBABEL2_FOUND AND Avogadro_FOUND AND EIGEN3_FOUND)
+if (OPENBABEL2_FOUND AND Avogadro_FOUND AND EIGEN2_FOUND)
   # avoid compilerwarnings about redefinitions
   # todo: use check_function_exits() ?
   message(STATUS "Kalzium molecular editor enabled")
@@ -43,9 +43,9 @@ if (OPENBABEL2_FOUND AND Avogadro_FOUND
     add_definitions(-DHAVE_SNPRINTF -DHAVE_STRCASECMP -DHAVE_STRNCASECMP)
   endif (WIN32)
   add_subdirectory(compoundviewer)
-else (OPENBABEL2_FOUND AND Avogadro_FOUND AND EIGEN3_FOUND)
+else (OPENBABEL2_FOUND AND Avogadro_FOUND AND EIGEN2_FOUND)
   message(STATUS "Kalzium molecular editor disabled")
-endif (OPENBABEL2_FOUND AND Avogadro_FOUND AND EIGEN3_FOUND)
+endif (OPENBABEL2_FOUND AND Avogadro_FOUND AND EIGEN2_FOUND)
 
 add_subdirectory(doc)
 add_subdirectory(src)
diff -rupN kalzium-16.08.3/compoundviewer/CMakeLists.txt kalzium-16.08.3-new/compoundviewer/CMakeLists.txt
--- kalzium-16.08.3/compoundviewer/CMakeLists.txt	2016-10-16 06:54:22.000000000 +0200
+++ kalzium-16.08.3-new/compoundviewer/CMakeLists.txt	2016-12-22 11:52:39.805923124 +0100
@@ -2,7 +2,7 @@ include(${Avogadro_USE_FILE})
 
 include_directories(
   ${CMAKE_CURRENT_BINARY_DIR}/..
-  ${EIGEN3_INCLUDE_DIR}
+  ${EIGEN2_INCLUDE_DIRS}
   ${OPENBABEL2_INCLUDE_DIR}
   )
 
diff -rupN kalzium-16.08.3/KalziumConfigureChecks.cmake kalzium-16.08.3-new/KalziumConfigureChecks.cmake
--- kalzium-16.08.3/KalziumConfigureChecks.cmake	2016-10-16 06:54:22.000000000 +0200
+++ kalzium-16.08.3-new/KalziumConfigureChecks.cmake	2016-12-22 11:37:37.017177818 +0100
@@ -4,17 +4,17 @@ include(CheckFunctionExists)
 macro_optional_find_package(OCaml)
 macro_optional_find_package(Libfacile)
 macro_optional_find_package(OpenBabel2)
-macro_optional_find_package(Eigen3)
 macro_optional_find_package(Avogadro 1.0.0 NO_MODULE)
 
 find_package(PkgConfig)
 pkg_check_modules(CHEMICAL_MIME_DATA chemical-mime-data)
+pkg_check_modules(EIGEN2 eigen2)
 
 check_include_files(ieeefp.h HAVE_IEEEFP_H)
 
 macro_bool_to_01(LIBFACILE_FOUND HAVE_FACILE)
 macro_bool_to_01(OPENBABEL2_FOUND HAVE_OPENBABEL2)
-macro_bool_to_01(EIGEN3_FOUND HAVE_EIGEN)
+macro_bool_to_01(EIGEN2_FOUND HAVE_EIGEN)
 macro_bool_to_01(Avogadro_FOUND HAVE_AVOGADRO)
 
 # at the end, output the configuration
@@ -26,7 +26,7 @@ configure_file(
 macro_log_feature(OCAML_FOUND "OCaml" "OCaml is needed by Kalzium for the Equation Solver" "http://caml.inria.fr/" FALSE "" "")
 macro_log_feature(LIBFACILE_FOUND "LibFacile" "libfacile is needed by Kalzium for the Equation Solver." "http://www.recherche.enac.fr/log/facile/" FALSE "" "")
 macro_log_feature(OPENBABEL2_FOUND "OpenBabel2" "OpenBabel is needed by Kalzium for the 3D-molecule viewer" "http://openbabel.sourceforge.net/" FALSE "2.2" "")
-macro_log_feature(EIGEN3_FOUND "Eigen3" "A generic C++ template library for dense and sparse matrices" "http://eigen.tuxfamily.org" FALSE "3.0.0" "")
+macro_log_feature(EIGEN2_FOUND "Eigen2" "A generic C++ template library for dense and sparse matrices" "http://eigen.tuxfamily.org" FALSE "2.0.0" "")
 macro_log_feature(Avogadro_FOUND "Avogadro" "Advanced molecular editor" "http://avogadro.openmolecules.net" FALSE "1.0" "")
 macro_log_feature(CHEMICAL_MIME_DATA_FOUND "Chemical mime data" "Needed to open CML molecules from the file manager" "http://chemical-mime.sourceforge.net/" FALSE "" "")
 
diff -rupN kalzium-16.08.3/src/CMakeLists.txt kalzium-16.08.3-new/src/CMakeLists.txt
--- kalzium-16.08.3/src/CMakeLists.txt	2016-10-16 06:54:22.000000000 +0200
+++ kalzium-16.08.3-new/src/CMakeLists.txt	2016-12-22 11:12:50.985986130 +0100
@@ -23,7 +23,7 @@ if (OPENBABEL2_FOUND)
       )
    include_directories(${OPENBABEL2_INCLUDE_DIR})
 
-   if (EIGEN3_FOUND AND Avogadro_FOUND)
+   if (EIGEN2_FOUND AND Avogadro_FOUND)
 
       include(${Avogadro_USE_FILE})
 
@@ -35,8 +35,8 @@ if (OPENBABEL2_FOUND)
       kde4_add_ui_files(kalziumtools_SRCS
          tools/moleculeviewerwidget.ui
          )
-      include_directories(${EIGEN3_INCLUDE_DIR})
-   endif (EIGEN3_FOUND AND Avogadro_FOUND)
+      include_directories(${EIGEN2_INCLUDE_DIRS})
+   endif (EIGEN2_FOUND AND Avogadro_FOUND)
 endif (OPENBABEL2_FOUND)
 
 ## Kalzium calculator files
@@ -137,9 +137,9 @@ target_link_libraries(kalzium ${KDE4_KHT
 
 if (OPENBABEL2_FOUND)
    target_link_libraries(kalzium ${OPENBABEL2_LIBRARIES})
-   if (EIGEN3_FOUND AND Avogadro_FOUND)
+   if (EIGEN2_FOUND AND Avogadro_FOUND)
       target_link_libraries(kalzium ${QT_QTOPENGL_LIBRARY} compoundviewer avogadro)
-   endif (EIGEN3_FOUND AND Avogadro_FOUND)
+   endif (EIGEN2_FOUND AND Avogadro_FOUND)
 endif (OPENBABEL2_FOUND)
 
 if (LIBFACILE_FOUND)