From 43bf8f631954c403fb7a1997e0981243508604e1 Mon Sep 17 00:00:00 2001
From: jrm874 <43007996+jrm874@users.noreply.github.com>
Date: Fri, 10 Oct 2025 16:19:04 -0400
Subject: [PATCH] Choose between with and without Cartesian prod.

---
 SHCI/SHCI.cpp  | 68 +++++++++++++++++++++++++++++++++++++++-----------
 SHCI/input.cpp |  3 +++
 SHCI/input.h   |  2 ++
 3 files changed, 58 insertions(+), 15 deletions(-)

diff --git a/SHCI/SHCI.cpp b/SHCI/SHCI.cpp
index a54654a..07ad1b4 100644
--- a/SHCI/SHCI.cpp
+++ b/SHCI/SHCI.cpp
@@ -360,26 +360,64 @@ int main(int argc, char* argv[]) {
       }
     }
 
+    // Condition checking only if nonsymmetric determinants
+    if (nAlphaDets != nBetaDets && schd.alpha_beta_cartesian_product == false){
+      cout << "Number of alpha dets not equal to beta dets ("<<nAlphaDets<<") and ("<< nBetaDets <<")"<<endl;
+        exit(0);
+    }
+
     // Make HF determinant
-    Dets.resize(nAlphaDets*nBetaDets);
-    for (int i=0; i<nAlphaDets; i++) {
+    if (schd.alpha_beta_cartesian_product == true){
+      cout<< endl;
+      cout << "Running diagonalization with Cartesian product symmetrization" << endl; 
+      cout << "Subspace dimension: " << nAlphaDets * nBetaDets << endl; 
+      cout<< endl;
+      Dets.resize(nAlphaDets * nBetaDets);
+      for (int i=0; i<nAlphaDets; i++) {
       for (int j=0; j<nBetaDets; j++) {
-        Determinant& d = Dets[i*nBetaDets+j];
-        for (int a=0; a<nalpha; a++)
-          d.setocc(occAlpha[i][a]*2, true);
-        for (int a=0; a<nbeta; a++) 
-          d.setocc(occBeta[j][a]*2+1, true);
-
-
-        double E = d.Energy(I1, I2, coreE);
-        //pout << d << " Given Ref. Energy:    "
-        //     << format("%18.10f") % (E) << endl;
-        if (E < lowestEnergy) {
-          lowestEnergy = E;
-          lowestEnergyDet = i*nBetaDets+j;
+          Determinant& d = Dets[i*nBetaDets+j];
+          for (int a=0; a<nalpha; a++)
+            d.setocc(occAlpha[i][a]*2, true);
+          for (int a=0; a<nbeta; a++) 
+            d.setocc(occBeta[j][a]*2+1, true);
+
+
+          double E = d.Energy(I1, I2, coreE);
+          //pout << d << " Given Ref. Energy:    "
+          //     << format("%18.10f") % (E) << endl;
+          if (E < lowestEnergy) {
+            lowestEnergy = E;
+            lowestEnergyDet = i*nBetaDets+j;
+          }
         }
       }
     }
+
+    if (schd.alpha_beta_cartesian_product == false){
+      cout<< endl;
+      cout << "Running diagonalization WITHOUT Cartesian product symmetrization" << endl; 
+      cout << "Subspace dimension: " << nAlphaDets << endl; 
+      cout<< endl;
+      // Make HF determinant
+      Dets.resize(nAlphaDets);
+      for (int i=0; i<nAlphaDets; i++) {
+          Determinant& d = Dets[i];
+          for (int a=0; a<nalpha; a++)
+            d.setocc(occAlpha[i][a]*2, true);
+          for (int a=0; a<nbeta; a++) 
+            d.setocc(occBeta[i][a]*2+1, true);
+
+          double E = d.Energy(I1, I2, coreE);
+          //pout << d << " Given Ref. Energy:    "
+          //     << format("%18.10f") % (E) << endl;
+          if (E < lowestEnergy) {
+            lowestEnergy = E;
+            lowestEnergyDet = i;
+          }
+
+      }
+    }
+
   }
 
   HFoccupied.resize(1);
diff --git a/SHCI/input.cpp b/SHCI/input.cpp
index dab4ec3..6bf7ce3 100644
--- a/SHCI/input.cpp
+++ b/SHCI/input.cpp
@@ -121,6 +121,7 @@ void readInput(string input, std::vector<std::vector<int> >& occupied,
   schd.sampleNewDets = false;
   schd.precondition = false;
   schd.cdfciTol = 1e-12;
+  schd.alpha_beta_cartesian_product = false;
 
   schd.Bvalue = 0;
   schd.Bdirection.resize(0);
@@ -176,6 +177,8 @@ void readInput(string input, std::vector<std::vector<int> >& occupied,
       schd.ncore = atoi(tok[1].c_str());
     else if (boost::iequals(ArgName, "noio"))
       schd.io = false;
+    else if (boost::iequals(ArgName, "alpha_beta_cartesian_product"))
+      schd.alpha_beta_cartesian_product = true;
     else if (boost::iequals(ArgName, "dolcc"))
       schd.doLCC = true;
     else if (boost::iequals(ArgName, "io"))
diff --git a/SHCI/input.h b/SHCI/input.h
index 9a00cd6..0b22f93 100644
--- a/SHCI/input.h
+++ b/SHCI/input.h
@@ -108,11 +108,13 @@ struct schedule {
     & cdfci_on                                \
     & cdfciIter                               \
     & z_threshold                             \
+    & alpha_beta_cartesian_product            \
     & max_determinants;
   }
   // clang-format on
 
  public:
+  bool alpha_beta_cartesian_product;
   double davidsonTol;
   double davidsonTolLoose;
   rdmType RdmType;