Changelog

The format is based on Keep a Changelog, and uses Semantic Versioning.

[1.4.0] - 2026-08-14

Added

  • Automated Embedded Atoms Selection

    We added an embedded atoms selection module that automatically identifies the reactive part of a molecule. It provides primary selectors based on coordination changes, EEQBC atomic charge changes, and electronic structure changes, together with extenders (nearest-neighbor, distance, and full-molecule) to grow the selected embedded region.

  • Automated Active Space Selection

    We added automated active space selection tooling, including AVAS (Atomic Valence Active Space), orbital fingerprinting, and configurable active space selectors. These are integrated into new modular ground-state and reaction-path problem builders and modifiers, and include a consistent active space procedure that keeps the active space consistent across the points of a reaction path.

  • Avoid Region Mixing Pipek-Mezey Localizer

    We added a Pipek-Mezey localizer that discourages cross-region mixing. This is now the default localizer for Projection-Based Wavefunction-in-DFT (WF-in-DFT) embedding problems.

  • Møller-Plesset pertubation theory to 2nd order (MP2) Initial Ansatz

    We added the Møller-Plesset pertubation theory to 2nd order (MP2) ansatz as an initial state for VQE calculations. The MP2 ansatz is a circuit that mimics the MP2 wave function.

Changed

  • The default Molecular Orbital (MO) calculator has been changed from Hartree-Fock to MP2 in the full ground state problem builder.

Fixed

  • Fixed early stopping in the TRIM-CI calculator so that it now terminates correctly when the determinant pool can no longer be expanded or all determinants have been reached.

  • Added validation to TrimCIOptions to reject configurations where initial_number_of_determinants exceeds final_number_of_determinants, and corrected the TrimCIOptions docstring to match its actual attributes.

  • Fixed a bug in the reduced density matrix (RDM) calculation.

  • Fixed resuming (warm starting) of OO-FAST-VQE calculations.

  • Fixed a bug in the RandomGateSelector used during adaptive VQE ansatz growth.

[1.3.0] - 2026-06-24

Added

  • Classical Chemistry Calculators

    We added several new classical chemistry reference calculators including:

    • Second-order Møller-Plesset (MP2) ground-state problem calculator and reaction path problems calculator.

    • Coupled cluster (CCSD and CCSD(T)) ground-state problem calculator and reaction path problems calculator.

    • TRIM-CI (Truncated Restricted-active-space Interaction with Many-body perturbation) configuration interaction calculator.

    We also added the coupled cluster singles and doubles (CCSD) as a new molecular orbital calculator.

  • Tensor Network Simulation

    We added a new tensor network simulation module with support for both CPU and GPU backends.

  • GPU Acceleration

    We have added GPU-acceleration to the orbital optimization Hessian (supported on Linux and MLX support on macOS) We have also added the CuQuantum state-vector estimator for GPU-accelerated exact simulation.

  • Optional Extras for Hardware Backends

    Hardware backend dependencies (IBM, IQM, OQC, CUDA) have been restructured as pip optional extras. This means a bare pip install qrunch no longer pulls in heavy, backend-specific dependencies you may not need. Install only the extras required for your target hardware, e.g. pip install qrunch[iqm] to get the IQM backend working. Multiple extras can be combined: pip install qrunch[iqm, oqc]. To restore the previous behaviour where all backend dependencies are included, use pip install qrunch[all].

  • Shadow Grouper

    We added a Shadow grouper that creates groups by sampling the most important Pauli strings for the observable first.

  • Better shot utilisation

    We changed the definition of shots and added shot distributors with the new .with_total_estimator_shots(shots=1_000_000) method. The new method sets the total number of shots and distributes them across measurement groups, ensuring better use of the shot budget on hardware. The existing .with_estimator_shots(shots=1000) continues to work as before, setting the number of shots per call to the quantum computer or simulator. But deprecated in the next release.

  • Performance Improvements

    • Several general performance improvements.

    • Performance improvements for OO-FAST-VQE and OO-BEAST-PT2 VQE workflows.

[1.2.0] - 2026-05-22

Added

  • Rigetti Cepheus 108Q support via Amazon Braket.

  • Auxiliary energy contributions (DFT mean-field energies) for projective embedding problems.

  • Active electrons correlation energy property added on GroundStateProblemCalculatorResult

  • Verification that hardware backends function correctly on creation of a backend sampler or estimator.

  • Data persister support for the Configuration Interaction calculator.

  • Improved default for RI/Auxiliary basis sets.

  • VQE warm start utilities for starting VQE calculations from a previous result, a custom circuit, or a parameterized circuit.

Changed

  • Upgraded Qrunch to Python 3.12.

Fixed

  • Fixed measurement result bit ordering for IQM backends.

  • Fixed memory leak in RI integral evaluation.

  • Fixed support for Amazon Braket Hybrid Jobs.

[1.1.0] - 2026-03-03

Added

  • BEAST-PT2 (Second-Order Correction for BEAST-VQE)

    BEAST-VQE can now be augmented with a second-order perturbative correction to improve accuracy beyond the paired-electron approximation. The correction supports pair-breaking effects, single excitations, or both, and can be enabled directly in the calculator configuration.

  • Noisy Memory Restricted Simulator

    A new memory-restricted simulator can emulate physical quantum hardware, including user configured device data. It combines the standard memory restricted simulator with Monte Carlo sampling, to emulate hardware-like behavior based on calibration data.

  • GPU Acceleration

    We introduced a new GPU acceleration module with initial support for accelerated orbital rotations, providing improved performance for selected workflows.

  • Hardware Backend Improvements

    • Support for IBM NightHawk architecture devices (e.g., Miami).

    • Optional instance selection for IBM Quantum Platform backends.

    • Improved robustness of IQM backends when handling missing qubits or calibration data.

  • Performance Improvements

    • Faster mapping from second-quantized Hamiltonians to Pauli operators.

    • Performance improvements for FAST-VQE and BEAST-VQE workflows.

    • Reduced logging overhead in the memory-restricted simulator.

Deprecated

  • Tensor Hypercontraction integrals have been deprecated as it never worked to our satisfaction and it will be removed in a future release.

Fixed

  • Fixed a performance issue in even-handed projective-embedding calculations.