1#
2#   CheMPS2: a spin-adapted implementation of DMRG for ab initio quantum chemistry
3#   Copyright (C) 2013-2018 Sebastian Wouters
4#
5#   This program is free software; you can redistribute it and/or modify
6#   it under the terms of the GNU General Public License as published by
7#   the Free Software Foundation; either version 2 of the License, or
8#   (at your option) any later version.
9#
10#   This program is distributed in the hope that it will be useful,
11#   but WITHOUT ANY WARRANTY; without even the implied warranty of
12#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13#   GNU General Public License for more details.
14#
15#   You should have received a copy of the GNU General Public License along
16#   with this program; if not, write to the Free Software Foundation, Inc.,
17#   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
18#
19
20import numpy as np
21import sys
22import PyCheMPS2
23import ctypes
24
25# Set the seed of the random number generator and cout.precision
26Initializer = PyCheMPS2.PyInitialize()
27Initializer.Init()
28
29# Read in the FCIDUMP
30psi4group = 5 # c2v: see chemps2/Irreps.h
31filename  = b'../../tests/matrixelements/CH4.STO3G.FCIDUMP'
32orbirreps = np.array([-1, -1], dtype=ctypes.c_int) # CheMPS2 reads it in from FCIDUMP
33Ham = PyCheMPS2.PyHamiltonian( -1, psi4group, orbirreps, filename )
34
35# Define the symmetry sector
36TwoS  = 0    # Two times the targeted spin
37Nelec = 10   # The number of electrons
38Irrep = 0    # The targeted irrep
39
40# Setting up the Problem
41Prob = PyCheMPS2.PyProblem(Ham, TwoS, Nelec, Irrep)
42
43# Setting up the ConvergenceScheme
44# setInstruction(instruction, D, Econst, maxSweeps, noisePrefactor)
45OptScheme = PyCheMPS2.PyConvergenceScheme(2) # 2 instructions
46OptScheme.setInstruction(0,   30, 1e-10,  3, 0.1)
47OptScheme.setInstruction(1, 1000, 1e-10, 10, 0.0)
48
49# Do DMRG calculation
50theDMRG = PyCheMPS2.PyDMRG(Prob, OptScheme)
51EnergyDMRG = theDMRG.Solve()
52theDMRG.calc2DMandCorrelations()
53
54# Do FCI calculation
55Nel_up   = ( Nelec + TwoS ) / 2
56Nel_down = ( Nelec - TwoS ) / 2
57maxMemWorkMB = 10.0
58FCIverbose = 1
59theFCI = PyCheMPS2.PyFCI(Ham, Nel_up, Nel_down, Irrep, maxMemWorkMB, FCIverbose)
60GSvector = np.zeros([ theFCI.getVecLength() ], dtype=ctypes.c_double)
61GSvector[ theFCI.LowestEnergyDeterminant() ] = 1.0
62EnergyFCI = theFCI.GSDavidson(GSvector)
63theFCI.CalcSpinSquared(GSvector)
64TwoRDM = np.zeros([ Ham.getL()**4 ], dtype=ctypes.c_double)
65theFCI.Fill2RDM(GSvector, TwoRDM)
66RMSerror2DM = 0.0
67for orb1 in range(0, Ham.getL()):
68    for orb2 in range(0, Ham.getL()):
69        for orb3 in range(0, Ham.getL()):
70            for orb4 in range(0, Ham.getL()):
71                temp = TwoRDM[orb1 + Ham.getL()*(orb2 + Ham.getL()*(orb3 + Ham.getL()*orb4))] - theDMRG.get2DMA(orb1,orb2,orb3,orb4)
72                RMSerror2DM += temp*temp
73RMSerror2DM = np.sqrt(RMSerror2DM)
74print("Frobenius norm of the difference of the DMRG and FCI 2-RDMs =", RMSerror2DM)
75
76# Clean-up
77# theDMRG.deleteStoredMPS()
78theDMRG.deleteStoredOperators()
79del theFCI
80del theDMRG
81del OptScheme
82del Prob
83del Ham
84del Initializer
85
86# Check whether the test succeeded
87if ((np.fabs(EnergyDMRG - EnergyFCI) < 1e-8) and (RMSerror2DM < 1e-3)):
88    print("================> Did test 3 succeed : yes")
89else:
90    print("================> Did test 3 succeed : no")
91
92