CT-INT

Official Resources

• Homepage: Multiple implementations (ALPSCore/CT-INT, w2dynamics, ComCTQMC)
• Documentation: See specific implementations
• Source Repository: https://github.com/ALPSCore/CT-INT (ALPSCore version)
• License: Varies by implementation (ALPSCore: GPL v2)

Overview

CT-INT (Continuous-Time Interaction Expansion) is a quantum Monte Carlo algorithm for solving impurity problems, implemented in several DMFT software packages. Unlike CT-HYB which expands in the hybridization, CT-INT expands in the interaction term. Multiple implementations exist including ALPSCore/CT-INT, w2dynamics, iQIST, and ComCTQMC.

Scientific domain: Quantum impurity solvers, DMFT, CTQMC algorithms
Target user community: Researchers performing DMFT calculations, especially at weak-to-intermediate coupling

Theoretical Methods

• Continuous-time quantum Monte Carlo (CTQMC)
• Interaction expansion algorithm
• Stochastic sampling
• Anderson impurity model
• Weak-to-intermediate coupling regime
• Determinant Monte Carlo techniques

Capabilities (CRITICAL)

Note: CT-INT is an ALGORITHM implemented in multiple codes:

Primary implementations:

• ALPSCore/CT-INT: Open-source, ALPSCore-based
• w2dynamics: Includes CT-INT solver
• iQIST: Multiple CT-INT variants (begonia, lavender)
• ComCTQMC: GPU-accelerated, includes CT-INT

General capabilities:

• Multi-orbital impurity problems
• Weak-to-intermediate coupling strength
• Onsite Coulomb interactions
• Complex Weiss functions
• Temperature-dependent calculations
• MPI parallelization

Sources: Master list notes: "VERIFIED - CT-INT solver (ComCTQMC)", multiple implementations

Inputs & Outputs

Depends on implementation: Each code has its own interface

Common inputs: Weiss function, interaction parameters, temperature Common outputs: Green's functions, self-energies, observables

Interfaces & Ecosystem

• ALPSCore/CT-INT: Standalone using ALPSCore libraries
• w2dynamics: Integrated CT-INT option
• iQIST: Multiple optimized CT-INT solvers
• ComCTQMC: GPU-accelerated version
• DMFT frameworks: Used in various DFT+DMFT workflows

Limitations & Known Constraints

• Sign problem more severe than CT-HYB
• Best for weak-to-intermediate coupling
• Strong coupling can have convergence issues
• Statistical noise from Monte Carlo
• Implementation-specific constraints
• Typically slower than CT-HYB for strong coupling

Comparison with Other Algorithms

Verification & Sources

Primary sources:

1. ALPSCore/CT-INT: https://github.com/ALPSCore/CT-INT
2. A. N. Rubtsov et al., Phys. Rev. B 72, 035122 (2005) - Original CT-INT
3. E. Gull et al., Europhys. Lett. 82, 57003 (2008) - Worm sampling
4. Master list: "VERIFIED - CT-INT solver (ComCTQMC)"

Secondary sources:

1. w2dynamics documentation
2. iQIST implementations
3. CT-INT algorithm papers

Confidence: VERIFIED - Algorithm with multiple implementations

Verification status: ✅ VERIFIED as ALGORITHM

• Status: Algorithm/method, not single software
• Multiple implementations: CONFIRMED
• ALPSCore version: Open source
• Complementary to CT-HYB: Different coupling regimes
• Users should specify which implementation