diff --git a/pkgs/by-name/op/openmolcas/nevpt2.patch b/pkgs/by-name/op/openmolcas/nevpt2.patch
index 0033a17af196..a2ad9071c120 100644
--- a/pkgs/by-name/op/openmolcas/nevpt2.patch
+++ b/pkgs/by-name/op/openmolcas/nevpt2.patch
@@ -1,5 +1,3 @@
-diff --git a/src/gctime.c b/src/gctime.c
-index 34fcb6f..832459c 100644
 --- a/src/gctime.c
 +++ b/src/gctime.c
 @@ -1,14 +1,15 @@
@@ -20,3 +18,9 @@ index 34fcb6f..832459c 100644
     long time(), t;
     char *ctime();
     t = time ( (long *) 0);
+
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -1,4 +1,4 @@
+-cmake_minimum_required(VERSION 3.2)
++cmake_minimum_required(VERSION 3.5)
diff --git a/pkgs/by-name/op/openmolcas/package.nix b/pkgs/by-name/op/openmolcas/package.nix
index 17c1bddb1d38..6bca06f11afa 100644
--- a/pkgs/by-name/op/openmolcas/package.nix
+++ b/pkgs/by-name/op/openmolcas/package.nix
@@ -40,8 +40,8 @@ let
   qcmaquisSrc = fetchFromGitHub {
     owner = "qcscine";
     repo = "qcmaquis";
-    rev = "release-3.1.4"; # Must match tag in cmake/custom/qcmaquis.cmake
-    hash = "sha256-vhC5k+91IPFxdCi5oYt1NtF9W08RxonJjPpA0ls4I+o=";
+    rev = "9ff551fecbdbad43d17600c441a9c9bfb9811d3e"; # Current head of "nag-compiler-fix-internal" as pinned in OpenMolcas' Cmake
+    hash = "sha256-+EtfgYg6apREDOltXu8zfUbpuiV56k4RvuPAYO0fbsM=";
   };
 
   # NEVPT2 sources must be patched to be valid C code in gctime.c
@@ -64,13 +64,13 @@ let
 in
 stdenv.mkDerivation (finalAttrs: {
   pname = "openmolcas";
-  version = "25.10";
+  version = "26.02";
 
   src = fetchFromGitLab {
     owner = "Molcas";
     repo = "OpenMolcas";
     rev = "v${finalAttrs.version}";
-    hash = "sha256-z5RNLUP1DjvQ+LvNzOBwiPrYqGeZoPPbtaJv9gIefuM=";
+    hash = "sha256-+DU651GiGZRHdkLuGLCPU/95uOhG+kENCTi1T+8Hz1g=";
   };
 
   patches = [
@@ -159,6 +159,8 @@ stdenv.mkDerivation (finalAttrs: {
   # removed by autopatchelf
   noAuditTmpdir = true;
 
+  enableParallelBuilding = true;
+
   # Wrong store path in shebang (bare Python, no Python pkgs), force manual re-patching
   postFixup = ''
     for exe in $(find $out/bin/ -type f -name "*.py"); do
diff --git a/pkgs/by-name/op/openmolcas/qcmaquis.patch b/pkgs/by-name/op/openmolcas/qcmaquis.patch
index 0bfe34c648f7..42aa51a83fe2 100644
--- a/pkgs/by-name/op/openmolcas/qcmaquis.patch
+++ b/pkgs/by-name/op/openmolcas/qcmaquis.patch
@@ -1,29 +1,23 @@
 diff --git a/cmake/custom/nevpt2.cmake b/cmake/custom/nevpt2.cmake
-index 789739ec8..6c86a7b8c 100644
+index fa2ef9940f..ab6ce50eae 100644
 --- a/cmake/custom/nevpt2.cmake
 +++ b/cmake/custom/nevpt2.cmake
-@@ -67,6 +67,8 @@ list(APPEND NEVPT2CMakeArgs
-   "-DMOLCAS_BUILD_DIR=${PROJECT_BINARY_DIR}"
-   "-DCMAKE_Fortran_MODULE_DIRECTORY=${mod_dir}"
-   "-DDMRG_INCLUDE=${HDF5_QCM_INCLUDE}"
-+  "-DCMAKE_SKIP_BUILD_RPATH=ON"
-+      -DCMAKE_POLICY_VERSION_MINIMUM=3.5
-   )
-
- if(HDF5_ROOT)
-@@ -118,9 +119,7 @@ endif ()
-
+@@ -118,11 +118,8 @@ endif ()
+ 
  ExternalProject_Add(${EP_PROJECT}
                      PREFIX ${CUSTOM_NEVPT2_LOCATION}
 -                    GIT_REPOSITORY ${reference_git_repo}
 -                    GIT_TAG ${reference_git_commit}
+-                    GIT_PROGRESS 1
 -                    UPDATE_DISCONNECTED ${EP_SkipUpdate}
+-                    CMAKE_ARGS "${NEVPT2CMakeArgs}"
 +                    URL @nevpt2_src_url@
-                     CMAKE_ARGS "${NEVPT2CMakeArgs}"
++                    CMAKE_ARGS ${NEVPT2CMakeArgs}
                      INSTALL_DIR "${PROJECT_BINARY_DIR}/qcmaquis"
                     )
+ 
 diff --git a/cmake/custom/qcmaquis.cmake b/cmake/custom/qcmaquis.cmake
-index 5fd1ef207..8d2957c6e 100644
+index f144fcb4d9..5a7befd4e1 100644
 --- a/cmake/custom/qcmaquis.cmake
 +++ b/cmake/custom/qcmaquis.cmake
 @@ -77,6 +77,8 @@ list (APPEND QCMaquisCMakeArgs
@@ -35,26 +29,10 @@ index 5fd1ef207..8d2957c6e 100644
  )
  if (HDF5_ROOT)
    list (APPEND QCMaquisCMakeArgs
-@@ -274,10 +275,7 @@ if (NOT MAQUIS_DMRG_FOUND) # Does the opposite work?
-
-   ExternalProject_Add (${EP_PROJECT}
-                        PREFIX ${extprojpath}
--                       GIT_REPOSITORY ${reference_git_repo}
--                       GIT_TAG ${reference_git_commit}
--                       UPDATE_DISCONNECTED ${EP_SkipUpdate}
--
-+                       URL @qcmaquis_src_url@
-                        SOURCE_SUBDIR dmrg
-                        CMAKE_ARGS ${EP_CMAKE_ARGS}
-                        CMAKE_CACHE_ARGS ${EP_CMAKE_CACHE_ARGS}
-diff --git a/cmake/custom/qcmaquis.cmake b/cmake/custom/qcmaquis.cmake
-index 5fd1ef207..4291ec3d7 100644
---- a/cmake/custom/qcmaquis.cmake
-+++ b/cmake/custom/qcmaquis.cmake
-@@ -94,47 +94,9 @@ if (NOT MAQUIS_DMRG_FOUND) # Does the opposite work?
+@@ -94,47 +96,9 @@ if (NOT MAQUIS_DMRG_FOUND) # Does the opposite work?
      )
    endif (BOOST_ROOT)
-
+ 
 -  if (LINALG STREQUAL "Manual")
 -    target_files (LINALG_LIBRARIES_FILES ${LINALG_LIBRARIES})
 -    list (APPEND LINALG_LIBRARIES_FILES ${CMAKE_Fortran_IMPLICIT_LINK_LIBRARIES})
@@ -99,6 +77,19 @@ index 5fd1ef207..4291ec3d7 100644
 +  list (APPEND QCMaquisCMakeArgs
 +        "-DBLAS_LAPACK_SELECTOR=auto"
 +  )
-
+ 
    # Enabling source changes to keep ExternalProject happy
-   set (CMAKE_DISABLE_SOURCE_CHANGES OFF
+   set (CMAKE_DISABLE_SOURCE_CHANGES OFF)
+@@ -278,11 +242,7 @@ if (NOT MAQUIS_DMRG_FOUND) # Does the opposite work?
+ 
+   ExternalProject_Add (${EP_PROJECT}
+                        PREFIX ${extprojpath}
+-                       GIT_REPOSITORY ${reference_git_repo}
+-                       GIT_TAG ${reference_git_commit}
+-                       GIT_PROGRESS 1
+-                       UPDATE_DISCONNECTED ${EP_SkipUpdate}
+-
++                       URL @qcmaquis_src_url@
+                        SOURCE_SUBDIR dmrg
+                        CMAKE_ARGS ${EP_CMAKE_ARGS}
+                        CMAKE_CACHE_ARGS ${EP_CMAKE_CACHE_ARGS}
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 87981ddfbf7b..be7051913fbd 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -11622,6 +11622,10 @@ with pkgs;
     hdf5 = hdf5-fortran;
   };
 
+  openmolcas = callPackage ../by-name/op/openmolcas/package.nix {
+    boost = boost188;
+  };
+
   siesta-mpi = callPackage ../by-name/si/siesta/package.nix { useMpi = true; };
 
   ### SCIENCE/BIOLOGY