working ccd imaginary time propagation

coupled_cluster/ccd/itdccd.py

@@ -0,0 +1,36 @@
+from coupled_cluster import TDCCD
+from coupled_cluster.cc_helper import ( AmplitudeContainer)
+from coupled_cluster.integrators import RungeKutta4
+
+class ITDCCD(TDCCD):
+    """Performs imaginary time propagation for ground state calculations."""
+    def __call__(self, prev_amp, current_time):
+        o, v = self.system.o, self.system.v
+
+        prev_amp = AmplitudeContainer.from_array(self._amplitudes, prev_amp)
+        t_old, l_old = prev_amp
+
+        self.update_hamiltonian(current_time, prev_amp)
+
+        # Remove phase from t-amplitude list
+        t_old = t_old[1:]
+
+        t_new = [
+            - rhs_t_func(self.f, self.u, *t_old, o, v, np=self.np)
+            for rhs_t_func in self.rhs_t_amplitudes()
+        ]
+
+        # Compute derivative of phase
+        t_0_new = - self.rhs_t_0_amplitude(
+            self.f, self.u, *t_old, self.o, self.v, np=self.np
+        )
+        t_new = [t_0_new, *t_new]
+
+        l_new = [
+            - rhs_l_func(self.f, self.u, *t_old, *l_old, o, v, np=self.np)
+            for rhs_l_func in self.rhs_l_amplitudes()
+        ]
+
+        self.last_timestep = current_time
+
+        return AmplitudeContainer(t=t_new, l=l_new, np=self.np).asarray()