Computing <S^2> for wavefunction containers#457
Open
v-agamshayit wants to merge 29 commits into
Open
Conversation
v-agamshayit
requested review from
ConradJohnston,
nabbelbabbel,
sobolevnrm and
wavefunction91
as code owners
Contributor
There was a problem hiding this comment.
Pull request overview
Adds support for computing the expectation value ⟨S²⟩ on wavefunction containers using spin-dependent 1- and 2-RDMs (chemist/QDK Γ(p,q,r,s)=⟨a†ₚ a†ᵣ aₛ a_q⟩ convention), along with a comprehensive new C++ test suite validating the observable across hand-constructed RDMs and SCF→(CAS/SCI) workflows.
Changes:
- Implemented
WavefunctionContainer::compute_s_squared()and exposed it viaWavefunction::compute_s_squared(). - Documented the new API in
wavefunction.hpp. - Added
test_s_squared.cppwith analytical-state tests and end-to-end SCF+MACIS CAS/SCI tests.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
cpp/src/qdk/chemistry/data/wavefunction.cpp |
Implements ⟨S²⟩ evaluation from spin-dependent RDM blocks. |
cpp/include/qdk/chemistry/data/wavefunction.hpp |
Declares the new API and adds Doxygen documentation. |
cpp/tests/test_s_squared.cpp |
Adds analytical and integration tests to validate ⟨S²⟩ correctness. |
💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.
wavefunction91
requested changes
Apr 24, 2026
📊 Coverage Summary
Detailed Coverage ReportsC++ Coverage DetailsPython Coverage DetailsPybind11 Coverage Details |
Contributor
There was a problem hiding this comment.
Pull request overview
Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.
💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Contributor
There was a problem hiding this comment.
Pull request overview
Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.
💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Contributor
There was a problem hiding this comment.
Pull request overview
Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.
💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Comment on lines
+746
to
+748
| int norbs = static_cast<int>(one_rdm_aa.rows()); | ||
| double one_rdm_trace = one_rdm_aa.trace() + one_rdm_bb.trace(); | ||
|
|
Comment on lines
+717
to
+720
| if (!has_one_rdm_spin_dependent() || !has_two_rdm_spin_dependent()) { | ||
| throw std::runtime_error( | ||
| "Spin-dependent one- and two-body RDMs must be set to compute <S^2>"); | ||
| } |
Comment on lines
+746
to
+770
| int norbs = static_cast<int>(one_rdm_aa.rows()); | ||
| double one_rdm_trace = one_rdm_aa.trace() + one_rdm_bb.trace(); | ||
|
|
||
| // sum_{ij} Gamma(i,j,j,i): O(n^2) | ||
| auto sum_ijji = [norbs](const Eigen::VectorXd& vec) -> double { | ||
| double sum = 0.0; | ||
| for (int i = 0; i < norbs; ++i) { | ||
| for (int j = 0; j < norbs; ++j) { | ||
| int idx = i * norbs * norbs * norbs + j * norbs * norbs + j * norbs + i; | ||
| sum += vec[idx]; | ||
| } | ||
| } | ||
| return sum; | ||
| }; | ||
|
|
||
| // sum_{ij} Gamma(i,i,j,j): O(n^2) | ||
| auto sum_iijj = [norbs](const Eigen::VectorXd& vec) -> double { | ||
| double sum = 0.0; | ||
| for (int i = 0; i < norbs; ++i) { | ||
| for (int j = 0; j < norbs; ++j) { | ||
| int idx = i * norbs * norbs * norbs + i * norbs * norbs + j * norbs + j; | ||
| sum += vec[idx]; | ||
| } | ||
| } | ||
| return sum; |
Comment on lines
+528
to
+535
| /** | ||
| * @brief Compute the expectation value of the total spin-squared operator | ||
| * from the RDMs. | ||
| * | ||
| * @return The expectation value \f$\langle S^2 \rangle\f$ | ||
| * @throws std::runtime_error if the orbital basis declares no spin (S_z) axis | ||
| * (spin-blocked active-space RDMs cannot be generated) | ||
| */ |
Comment on lines
+1335
to
+1342
| /** | ||
| * @brief Compute the expectation value of the total spin-squared operator | ||
| * from the RDMs. | ||
| * | ||
| * @return The expectation value \f$\langle S^2 \rangle\f$ | ||
| * @throws std::runtime_error if the orbital basis declares no spin (S_z) axis | ||
| * (spin-blocked active-space RDMs cannot be generated) | ||
| */ |
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Added a function to compute <S^2> for arbitrary wavefunction containers using 1- and 2-RDMs consistent with the chemist's convention: Gamma(p,q,r,s) = <p^\dagger r^\dagger s q>.
Added some CASCI and SCI tests to verify correctness.