Add generalized active space CI solver with OpenMP C kernels

examples/mcscf/90_gasci_spin_supergroup.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python
+#
+# Author: Yi Deng <yideng@uchicago.edu>
+#
+
+"""Fixed-orbital GASCI with an explicit spin-supergroup set D."""
+
+import numpy
+
+from pyscf import gto
+from pyscf import scf
+from pyscf.mcscf import gasci
+
+
+mol = gto.M(
+    atom="N 0 0 0; N 0 0 1.10",
+    basis="sto-3g",
+    spin=0,
+    verbose=0,
+)
+mf = scf.RHF(mol).run()
+
+# Each row is (alpha occupations, beta occupations).  Rows are normalized to
+# lexicographic order and duplicates are removed before entering the C kernel.
+gas_restr = numpy.asarray([
+    [0, 2, 2, 0],
+    [1, 1, 1, 1],
+    [2, 0, 0, 2],
+], dtype=numpy.int32)
+
+mc = gasci.GASCI(
+    mf, 4, (2, 2), ncore=5,
+    gas_orbs=(2, 2),
+    gas_restr=gas_restr,
+    gas_restr_type="spin-supergroup",
+)
+mc.verbose = 4
+e_tot, e_gas, ci, _, _ = mc.kernel()
+
+print("GASCI total energy       = %.12f" % e_tot)
+print("GASCI active-space energy = %.12f" % e_gas)
+print("GAS determinant count     = %d" % ci.size)
+print("GAS space information     = %s" % mc.gas_space_info())

examples/mcscf/91_gas_restriction_types.py

@@ -0,0 +1,38 @@
+#!/usr/bin/env python
+#
+# Author: Yi Deng <yideng@uchicago.edu>
+#
+
+"""Normalize the four supported GAS restriction input formats."""
+
+import numpy
+
+from pyscf.mcscf import addons_gas
+
+
+gas_orbs = (2, 2)
+nelec = (2, 2)
+
+spin_supergroups = numpy.asarray([
+    [2, 0, 0, 2],
+    [1, 1, 1, 1],
+    [0, 2, 2, 0],
+    [1, 1, 1, 1],  # Duplicate rows are removed.
+])
+supergroups = numpy.asarray([[2, 2]])
+cumulative_occ = numpy.asarray([[2, 2], [4, 4]])
+
+for restriction_type, restriction in (
+        ("spin-supergroup", spin_supergroups),
+        ("supergroup", supergroups),
+        ("cumulative-occ", cumulative_occ)):
+    blocks = addons_gas.normalize_gas_restr(
+        gas_orbs, nelec, restriction, restriction_type)
+    print("%-17s ->\n%s" % (restriction_type, blocks))
+
+ras_blocks = addons_gas.normalize_gas_restr(
+    (1, 2, 1), nelec,
+    {"max_holes": 1, "max_particles": 1},
+    "ras",
+)
+print("ras               ->\n%s" % ras_blocks)

examples/mcscf/92_gasci_multiroot_rdm.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python
+#
+# Author: Yi Deng <yideng@uchicago.edu>
+#
+
+"""Multiroot GASCI with cumulative restrictions and state-resolved RDMs."""
+
+import numpy
+
+from pyscf import gto
+from pyscf import scf
+from pyscf.mcscf import gasci
+
+
+mol = gto.M(
+    atom="N 0 0 0; N 0 0 1.10", basis="sto-3g", spin=0, verbose=0)
+mf = scf.RHF(mol).run()
+
+# Each row gives the lower and upper cumulative electron occupation after
+# adding the corresponding GAS subspace.
+mc = gasci.GASCI(
+    mf, 4, (2, 2), ncore=5,
+    gas_orbs=(2, 2),
+    gas_restr=[[1, 3], [4, 4]],
+    gas_restr_type="cumulative-occ",
+)
+mc.fcisolver.nroots = 3
+mc.verbose = 4
+energies, _, _, _, _ = mc.kernel()
+
+for state, energy in enumerate(numpy.asarray(energies).reshape(-1)):
+    dm1, dm2 = mc.make_gasdm12(state=state)
+    ss, multiplicity = mc.spin_square(state=state)
+    pair_trace = numpy.einsum("pprr", dm2).real
+    print("state %d  E = %.12f  Tr(D1) = %.8f  S^2 = %.8f  mult = %.4f" %
+          (state, energy, numpy.trace(dm1), ss, multiplicity))
+    print("state %d  Tr_pair(D2) = %.8f" % (state, pair_trace))
+
+tdm1, tdm2 = mc.trans_gasdm12(bra_state=0, ket_state=2)
+print("transition 0 -> 2: ||D1|| = %.8f  ||D2|| = %.8f" %
+      (numpy.linalg.norm(tdm1), numpy.linalg.norm(tdm2)))
+
+_, natural_occ = mc.get_gas_natorb(state=0)
+_, pseudo_occ = mc.get_gas_pseudo_natorb(state=0)
+print("natural occupations        = %s" % natural_occ)
+for igas, occupations in enumerate(pseudo_occ):
+    print("GAS%d pseudo-natural occupations = %s" %
+          (igas + 1, occupations))

pyscf/lib/CMakeLists.txt

@@ -1,6 +1,77 @@
 cmake_minimum_required (VERSION 3.5)
 project (pyscf_forge)
 
+# Build only the GAS FCI kernel library.  This mode is intended for
+# reproducible local kernel builds and deliberately bypasses unrelated
+# dependencies such as BLAS, FFTW, and the other PySCF-forge extensions.
+option(
+  BUILD_GAS_FCI_ONLY
+  "Configure only the GAS FCI shared library"
+  OFF
+)
+
+option(ENABLE_OPENMP "Compiling C extensions with openmp" ON)
+
+function(add_gas_fci_library)
+  set(GAS_FCI_SOURCE_FILES
+      mcscf/fci_string_gas.c
+      mcscf/fci_contract_gas.c
+      mcscf/fci_hdiag_gas.c
+      mcscf/fci_rdm_gas.c
+  )
+
+  add_library(clib_fci_gas SHARED ${GAS_FCI_SOURCE_FILES})
+
+  target_include_directories(clib_fci_gas PRIVATE
+      ${CMAKE_CURRENT_SOURCE_DIR}/mcscf
+  )
+
+  target_compile_features(clib_fci_gas PRIVATE c_std_11)
+
+  if(CMAKE_C_COMPILER_ID MATCHES "GNU|Clang")
+    target_compile_options(clib_fci_gas PRIVATE
+        -Wall
+        -Wextra
+        -Wpedantic
+    )
+  endif()
+
+  target_link_libraries(clib_fci_gas PRIVATE m)
+
+  if(ENABLE_OPENMP AND TARGET OpenMP::OpenMP_C)
+    target_link_libraries(clib_fci_gas PRIVATE OpenMP::OpenMP_C)
+  endif()
+
+  set_target_properties(clib_fci_gas PROPERTIES
+      LINKER_LANGUAGE C
+      C_STANDARD 11
+      C_STANDARD_REQUIRED ON
+      C_EXTENSIONS OFF
+      CLEAN_DIRECT_OUTPUT 1
+      LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}
+      OUTPUT_NAME "fci_gas"
+  )
+endfunction()
+
+if(BUILD_GAS_FCI_ONLY)
+  if(NOT ENABLE_OPENMP)
+    message(FATAL_ERROR
+        "BUILD_GAS_FCI_ONLY=ON requires ENABLE_OPENMP=ON"
+    )
+  endif()
+
+  find_package(OpenMP REQUIRED COMPONENTS C)
+
+  if(NOT TARGET OpenMP::OpenMP_C)
+    message(FATAL_ERROR
+        "OpenMP was reported as found, but OpenMP::OpenMP_C is unavailable"
+    )
+  endif()
+
+  add_gas_fci_library()
+  return()
+endif()
+
 set(CMAKE_VERBOSE_MAKEFILE OFF)
 if (NOT CMAKE_BUILD_TYPE)
   set(CMAKE_BUILD_TYPE RELWITHDEBINFO)
@@ -71,7 +142,6 @@ find_package(BLAS REQUIRED)
 #find_package (LAPACK REQUIRED)
 
 # OpenMP
-option(ENABLE_OPENMP "Compiling C extensions with openmp" ON)
 set(OPENMP_C_PROPERTIES "")
 if(ENABLE_OPENMP)
   find_package(OpenMP)
@@ -112,6 +182,9 @@ else ()
   set(CMAKE_INSTALL_RPATH "\$ORIGIN:\$ORIGIN/deps/lib:\$ORIGIN/deps/lib64")
 endif ()
 
+# Build the GAS FCI kernel library as part of the normal PySCF-forge build.
+add_gas_fci_library()
+
 # Build the occri library (optional - depends on availability of FFTW, OpenMP)
 option(BUILD_OCCRI "Build OCCRI C extension (requires FFTW, OpenMP)" ON)