Welcome to ChemTensor’s documentation!

ChemTensor is an efficient tensor network library for electronic structure calculations of chemical systems (typically small molecules). It is based on the matrix product state (MPS) and tree tensor network state (TTNS) formalism and variants of DMRG.

ChemTensor is written in C for performance reasons. The file basic_dmrg_fermi_hubbard.c contains a standalone demonstration of constructing the Fermi-Hubbard model Hamiltonian as MPO and running DMRG.

ChemTensor also offers a Python 3 interface for more straightforward accessibility and experimentation.

Examples

Examples using the Python interface:

• Constructing an MPO from a sum of operator chains
• Constructing a TTNO from a sum of operator chains
• Fermi-Hubbard model Hamiltonian and DMRG
• Water molecule
• Operator average

Python API

• Python API reference
  • MPO
  • MPS
  • OpChain
  • TTNO
  • construct_bose_hubbard_1d_mpo()
  • construct_fermi_hubbard_1d_mpo()
  • construct_heisenberg_xxz_1d_mpo()
  • construct_ising_1d_mpo()
  • construct_molecular_hamiltonian_mpo()
  • construct_mpo_from_opchains()
  • construct_random_mps()
  • construct_spin_molecular_hamiltonian_mpo()
  • construct_ttno_from_opchains()
  • decode_quantum_number_pair()
  • dmrg()
  • encode_quantum_number_pair()
  • get_max_openmp_threads()
  • operator_average_coefficient_gradient()

C source code

• Common definitions (C code)
  • CT_MEM_DATA_ALIGN
  • ct_malloc()
  • ct_free()
  • ct_calloc()
  • scomplex
  • dcomplex
  • numeric_type
  • sizeof_numeric_type()
  • numeric_real_type()
  • numeric_one()
  • numeric_zero()
  • numeric_neg_one()
  • numeric_from_double()

• Dense and sparse tensors (C code)
  • Dense tensors
  • Block-sparse tensors
  • SU(2) symmetric tensors

• Quantum states (C code)
  • Matrix product states (MPS)
  • Tree tensor network states (TTNS)

• Quantum operators (C code)
  • Symbolic operator chains
  • Local operators
  • Matrix product operators (MPOs)
  • Tree tensor network operators (TTNOs)
  • Quantum Hamiltonians

• Tensor network algorithms (C code)
  • Virtual bonds
  • Chain topology
  • Tree topology
  • DMRG algorithm
  • Gradients
  • Tensor hypercontraction

• Utility functions and data structures (C code)
  • General utility functions
  • Queues
  • Linked lists
  • Hash tables
  • Abstract (symbolic) graphs
  • Bipartite graphs and Hopcroft-Karp algorithm
  • Integer linear algebra operations
  • Krylov subspace algorithms
  • Random number generation
  • Timing utility functions