[WIP] How to build a vibrational Hamiltonian #1402

soranjh · 2025-06-10T21:43:35Z

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github-actions · 2025-06-10T21:43:45Z

👋 Hey, looks like you've updated some demos!

🐘 Don't forget to update the dateOfLastModification in the associated metadata files so your changes are reflected in Glass Onion (search and recommendations).

Please hide this comment once the field(s) are updated. Thanks!

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.py

austingmhuang

Thanks @soranjh, it is in good shape. Please update the PR description and mark it ready for review (instead of WIP) so that the website can build as well.

austingmhuang · 2025-06-26T13:22:11Z

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.json

+    "dateOfPublication": "2024-12-05T00:00:00+00:00",
+    "dateOfLastModification": "2024-12-06T00:00:00+00:00",


Please update to current date

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.py

austingmhuang · 2025-06-26T14:29:26Z

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.py

+# operators, respectively. There are several ways to construct the potential energy operator which
+# lead to different representation of the vibrational Hamiltonian. Here we explain some of these


There are several ways to construct the potential energy operator which lead to different representation of the vibrational Hamiltonian.

I thought we always construct the PES the same way, just that the Christiansen form uses the PES as-is whereas the Taylor form uses the taylor expansion of the PES?

austingmhuang · 2025-06-26T14:33:07Z

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.py

+different representations of vibrational Hamiltonians. We also briefly discuss the implementation of
+the Hamiltonian in an interesting quantum algorithm for computing the vibrational dynamics of a
+molecule.


We also briefly discuss the implementation of
the Hamiltonian in an interesting quantum algorithm for computing the vibrational dynamics of a
molecule.

The demo simply constructs the Christiansen and Taylor hamiltonians, but doesn't actually use them in any quantum algorithm to compute the vibrational dynamics.

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.json

austingmhuang · 2025-06-26T14:33:56Z

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.json

+    "previewImages": [
+        {
+            "type": "thumbnail",
+            "uri": "/_static/demo_thumbnails/regular_demo_thumbnails/thumbnail_how_to_build_spin_hamiltonians.png"
+        },
+        {
+            "type": "large_thumbnail",
+            "uri": "/_static/demo_thumbnails/large_demo_thumbnails/thumbnail_large_how_to_build_spin_hamiltonians.png"
+        }


Reminder to update this as well.

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.py

ddhawan11

Thanks @soranjh, Do we also want to add bosonic Hamiltonian here or leave it just at christiansen and Taylor forms?

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.py

ddhawan11 · 2025-06-26T14:54:20Z

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.py

+# where :math:`M` represents the number of normal modes and :math:`N` is the number of modals. The
+# coefficients :math:`C` represent n-mode integrals which depend on the :math:`n`-mode contribution
+# of the potential energy, :math:`V_n`, defined above.


Should we mention here that for Christiansen Hamiltonian, we truncate the number of bosonic excitations to 2? As for the normal bosonic representation, we can set the number of modals to be higher.

Yes, feel free to add it here and I will merge it.

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.py

Co-authored-by: Austin Huang <austin.huang@xanadu.ai> Co-authored-by: Diksha Dhawan <40900030+ddhawan11@users.noreply.github.com>

austingmhuang · 2025-07-08T13:41:46Z

demonstrations/tutorial_how_to_build_vibrational_hamiltonians.py

+# that uses the :class:`~.pennylane.qchem.VibrationalPES` object directly and builds the 
+# Christiansen Hamiltonian in qubit representation.
+
+h_christiansen = qml.qchem.vibrational.christiansen_hamiltonian(pes,n_states=4)


Suggested change

h_christiansen = qml.qchem.vibrational.christiansen_hamiltonian(pes,n_states=4)

h_christiansen = qml.qchem.vibrational.christiansen_hamiltonian(pes, n_states=4)

soranjh added 4 commits June 6, 2025 16:59

add intro

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add christiansen

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add pes code

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add hamiltonians

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soranjh mentioned this pull request Jun 12, 2025

Upgrade vibrional hamiltonian docs PennyLaneAI/pennylane#6918

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Merge branch 'master' into vibrational_hamiltonian

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soranjh commented Jun 25, 2025

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soranjh requested review from ddhawan11 and austingmhuang June 25, 2025 20:02

Merge branch 'master' into vibrational_hamiltonian

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soranjh and others added 5 commits July 3, 2025 09:44

Apply suggestions from code review

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Co-authored-by: Austin Huang <austin.huang@xanadu.ai> Co-authored-by: Diksha Dhawan <40900030+ddhawan11@users.noreply.github.com>

add conc and refs

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austingmhuang reviewed Jul 8, 2025

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		"dateOfPublication": "2024-12-05T00:00:00+00:00",
		"dateOfLastModification": "2024-12-06T00:00:00+00:00",

		# operators, respectively. There are several ways to construct the potential energy operator which
		# lead to different representation of the vibrational Hamiltonian. Here we explain some of these

	h_christiansen = qml.qchem.vibrational.christiansen_hamiltonian(pes,n_states=4)
	h_christiansen = qml.qchem.vibrational.christiansen_hamiltonian(pes, n_states=4)

[WIP] How to build a vibrational Hamiltonian #1402

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soranjh commented Jun 10, 2025

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