Features

The main features of the core components (i.e., quantum impurity solvers) of the iQIST software package are summarized as follows:

• Model
  1. Density-density interaction
  2. General interaction (Slater or Kanamori scheme)
  3. Spin-orbital coupling and crystal field splitting
  4. Hubbard-Holstein model
  5. Frequency-dependent Coulomb interaction

• Measurement tricks
  1. Orthogonal polynomial representation (Legendre polynomials)
  2. Improved estimator for self-energy function

• Observables
  1. Single-particle Green's function in imaginary time space
  2. Single-particle Green's function in matsubara frequency space
  3. Two-particle correlation function in matsubara frequency space (experimental)
  4. Self-energy function in matsubara frequency space
  5. Histogram of perturbation expansion order
  6. Kurtosis and skewness of perturbation expansion order
  7. Kinetic and potential energies
  8. Orbital occupation numbers
  9. Double occupation numbers
  10. Magnetic moment
  11. Atomic state probability
  12. Spin-spin correlation function in imaginary time space
  13. Spin-spin correlation function in matsubara frequency space
  14. Orbital-orbital correlation function in imaginary time space
  15. Orbital-orbital correlation function in matsubara frequency space
  16. Fidelity susceptibility
  17. Kinetic energy fluctuation $\langle k^2\rangle - \langle k\rangle^2 - \langle k\rangle$

• Fast algorithms
  1. Segment algorithm for density-density interaction
  2. Divide-and-conquer algorithm
  3. Sparse matrix multiplication
  4. Good quantum numbers ($N, S_z, J_z$, PS)
  5. Lazy trace evaluation
  6. Dynamical truncation approximation

• Parallelism
  1. MPI
  2. OpenMP

• Preprocessing
  1. Atomic eigenvalue problem solver