Fix(deltaspin): enable DeltaSpin constraint energy calculation for PW basis

- cal_escon(): replace is_Mi_converged gate with lambda_/Mi_ empty check
  to prevent segfault when uninitialized
- elecstate_pw: add get_spin_constrain_energy() override so PW basis
  computes DeltaSpin constraint energy (previously returned 0.0)
- elecstate_pw.h: declare get_spin_constrain_energy() override

Note: this fix enables escon computation for PW DeltaSpin but
lambda values from BFGS optimizer may differ from accel branch
due to energy functional convention differences. Full convergence
with accel requires lambda_loop.cpp migration.

Author: dyzheng

source/source_estate/elecstate_pw.cpp

@@ -8,6 +8,7 @@
 #include "source_base/timer.h"
 #include "source_hamilt/module_xc/xc_functional.h"
 #include "source_io/module_parameter/parameter.h"
+#include "source_lcao/module_deltaspin/spin_constrain.h"
 #include "source_pw/module_pwdft/vnl_pw.h"
 
 namespace elecstate {
@@ -56,6 +57,14 @@ ElecStatePW<T, Device>::~ElecStatePW()
     delmem_complex_op()(this->wfcr_another_spin);
 }
 
+template<typename T, typename Device>
+double ElecStatePW<T, Device>::get_spin_constrain_energy()
+{
+    spinconstrain::SpinConstrain<std::complex<double>>& sc
+        = spinconstrain::SpinConstrain<std::complex<double>>::getScInstance();
+    return sc.cal_escon();
+}
+
 template<typename T, typename Device>
 void ElecStatePW<T, Device>::init_rho_data() 
 {

source/source_estate/elecstate_pw.h

@@ -36,6 +36,8 @@ class ElecStatePW : public ElecState
 
     virtual void cal_tau(const psi::Psi<T, Device>& psi);
 
+    double get_spin_constrain_energy() override;
+
     //! calculate becsum for uspp
     void cal_becsum(const psi::Psi<T, Device>& psi);
 

source/source_lcao/module_deltaspin/spin_constrain.cpp

@@ -45,7 +45,7 @@ template <typename TK>
 double SpinConstrain<TK>::cal_escon()
 {
     this->escon_ = 0.0;
-    if (!this->is_Mi_converged)
+    if (this->lambda_.empty() || this->Mi_.empty())
     {
         return this->escon_;
     }