Questions tagged [chemistry]

For questions regarding (or related to) applications of quantum information theory in chemistry or applications of chemistry in quantum computing.

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Can someone explain how Qiskit defines the electronic dipole moments?

The Qiskit API defines the electronic dipole moment as $$ \hat{d} = \sum_{p,q} d_{pq}^x a_p^\dagger a_q , $$ where $d_{pq}^x,d_{pq}^y,$ and $d_{pq}^z$ are the Cartesian components of the vector $$ \...
squareroottwo's user avatar
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Qiskit - Approximation of Hamiltonian energy via QPE

I'm trying to study QPE with the motivation of obtaining eigenvalues of Hamiltonian, i.e. energies of a system. My problem is, that while np.linalg.eig and VQE are agreeing on the lowest energy, ...
Eenoku's user avatar
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Quantum simulation for solving complicated hamiltonians exactly

Currently an undergrad in chemsitry taking a quantum computing class and I'm looking for a topic for small project involving literary review of QC articles. I was wondering if quantum computing can be ...
quantaq's user avatar
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Error when importing qiskit_nature.algorithms.(GroundStateEigensolver, NumPyMinimumEigensolverFactory)

I'm trying to import the following elements: from qiskit_nature.algorithms import (GroundStateEigensolver, NumPyMinimumEigensolverFactory) But it shows the error: AttributeError: module 'sklearn....
劉承瀚's user avatar
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Only use the specific parameters (angles) in variational quantum eigensolver

I’m following the tutorial (https://qiskit.org/textbook/ch-applications/vqe-molecules.html) to construct the VQE circuit. In this tutorial, it used the classical optimizer like “COBYLA, SPSA, SLSQP” ...
劉承瀚's user avatar
2 votes
1 answer
68 views

Logical vs Physical Qubits for Quantum Chemistry DFT

How many physical qubits are required per logical qubit in a typical Density Functional Theory implementation for a large number of atoms?
user23301's user avatar
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1 answer
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Remove Orbitals in FreezeCoreTransformer (qiskit)

In Qiskit's VQE tutorial, the FreezeCoreTransformer is used and some orbitals are removed. In the particular case of LiH, they remove [-2,-3] orbitals. Why are the orbitals indexed in this way? How ...
Maria Gabriela Oliveira's user avatar
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Reproducing Hydrogen Molecule Hamiltonian in OpenFermion

I am learning quantum chemistry at the moment and I'm trying to understand the Hamiltonian generated by the OpenFermion package. I'm now stuck at understanding how openfermion calculates the ...
user avatar
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How does the Active Space Transform work theoretically?

I have a question about the ActiveSpaceTransformer which is used in vqe calculations for a molecule of LiH in Qiskit. In the documentation the inactive Fock operator is defined.I don't understand why ...
Natale Matranga's user avatar
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1 answer
121 views

If you had a 1000 qubit NISQ machine with arbitrary connectivity, what would you do?

Many current devices are constrained to nearest neighbor connectivity or small system sizes, but suppose that a NISQ machine with 99-99.5% level two-qubit gate fidelities and arbitrary connectivity ...
shixian105's user avatar
3 votes
1 answer
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Efficiently compute $\langle 0^{\otimes n} | e^{iA} H e^{-iB} |0^{\otimes n} \rangle$ in Qiskit

From this SE question and this Qiskit tutorial, I understand how to compute the expectation such in the form of $\langle \psi|H|\psi\rangle$ or $\langle 0^{\otimes n} |e^{iA} H e^{-iA}|0^{\otimes n} \...
Firepanda's user avatar
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Obtaining non spin traced 3 and 4-RDM in MO basis from MP2 calculation

For an algorithm to be implemented on qiskit, I am trying to obtain 3 and 4 RDMs after an MP2 calculation. I have been trying a lot to find any module or package that could calculate these quantities ...
Kurious's user avatar
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2 answers
520 views

Why does Parity mapping allow 2 qubit reduction?

when mapping from fermionic to qubit hamiltonian, using Parity mapper allow us to reduce 2 qubit in the final hamiltonian. I would like to understand which kind of symmetries are being used and how it ...
bjail66's user avatar
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Jordan-Wigner map for ionic molecule H_2^+

I want to derive the Hamiltonian of the ion molecule $H_2^+$ by making use of Jordan-Wigner map. Thus, I used qiskit nature. I wrote down the same command given in qiskit nature. The only difference ...
DaeKil Park's user avatar
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1 answer
207 views

Qiskit - nuclear repulsion energy derivative

I know a function in PSI4 computing a nuclear repulsion energy derivative located in psi4.core.Molecule. Is there a possibility to access such function from Qiskit interface? By this "interface&...
Eenoku's user avatar
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Evaluating $\texttt{FermionOperator}$ equality in Openfermion

Apologies if this is the wrong place to ask this kind of question. I have a simple question about Openfermion. I have two normal ordered FermionOperators ...
Solarflare0's user avatar
3 votes
1 answer
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How to construct a parameterised UCCSD ansatz?

I want to try the UCC ansatz for problems other than quantum chemistry. For that I want to 'extract' the UCC ansatz (say from Qiskit) and supply it to my own VQE: I need a parameterised circuit where ...
quantum's user avatar
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4 votes
1 answer
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Is molecule simulation by quantum computing critical for drug discovery?

It is often said that the molecule simulation for drug discovery will be one of the most important applications of Quantum Computing (QC). As we all know that the entire process of new drug discovery ...
david's user avatar
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Roughly speaking, How many qubits will be needed to study (or simulate) a molecule such as: C29H31N7O?

It is often said that one of the early applications for Quantum Computers will be drug discovery. Q: Roughly speaking, How many qubits will be needed to study (or simulate) a molecule such as: $C_{29}...
david's user avatar
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Save output, wavefunction file and orbital information in Qiskit

I am going through LiH ground state energy calculation. I would like to know how to save the output file in Qiskit as one would do in classical computing using software like Gaussian or Psi4. Also, ...
Rag's user avatar
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636 views

How to calculate the Hartree-Fock energy in Qiskit?

I am wondering how to calculate the Hartree-Fock energy efficiently using Qiskit. For one can get the Hartree-Fock state efficiently in Qiskit, however, it seems that it is not so obvious to get the ...
ironmanaudi's user avatar
5 votes
1 answer
649 views

Molecular orbitals in Qiskit

During the same minute as asking this question, I also asked this at Matter Modeling SE. In Qiskit, each qubit corrrespond to one spin orbital. For example, the $\text{N}_2$ molecule have 10 molecular ...
ironmanaudi's user avatar
2 votes
1 answer
166 views

From general Hamiltonian to Ising Hamiltonian

I would like to convert my qubit hamiltonian fom the HeH+ system that I have obtained using Qiskit to an Ising or QUBO model. I have seen multiples examples from QUBO to Qubit Hamiltonian but on the ...
bjail66's user avatar
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Why the last IBMQ job of my VQE have just one circuit?

I am running a VQE over the H2 molecule on ibmq_quito and I set a callback function to save all jobs id's of all iterations. When I check the penultimate job (and the previous ones), I have 2 circuits ...
bjail66's user avatar
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Is VQE or one of its variations enough to help with medicine development?

One of the reasons quantum computing is often hyped in media is because of how it'll help with vaccine and medicine development. For example, this article in Financial Express and this other in ...
epelaez's user avatar
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4 votes
2 answers
273 views

How do I identify a VQE job run in real hardware?

I am running a VQEUCCFactory for H2 on a real hardware device. ...
bjail66's user avatar
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6 votes
1 answer
289 views

Use one_body_integrals to know which orbitals to freeze in ElectronicStructureProblem

In exercise 5 of the this year's IBM Quantum Challenge, you need to use the FreezeCoreTransformer (along two_qubit_reduction and ...
epelaez's user avatar
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2 votes
1 answer
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Add FreezeCoreOrbitals on ElectronicStructureProblem

I want to freeze core orbitals of my molecule and I know ElectronicStructureProblem has the possibility (es_problem = ElectronicStructureProblem(driver=driver, q_molecule_transformers=...
bjail66's user avatar
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1 vote
1 answer
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How do I work with Gaussian in Qiskit?

I am trying to run this Qiskit Nature tutorial (Vibrational Structure) and it uses the GaussianForceDriver. Every time I run the Gaussian job from Qiskit I get this message: ...
bjail66's user avatar
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Getting the current variational parameters in Qiskit

I am right now using variational quantum eigensolver (VQE) to calculate the ground state of some molecules, like H2, by qiskit. The quesiton is that how to get the current parameters of the varaional ...
ironmanaudi's user avatar
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0 answers
194 views

Molecular Docking using Quantum Computing

I would like to ask if somebody could suggest me a pair of ligand-Protein which had been validated and the corresponding resulting drug is already being used commercially. I am interested in ...
QuantumNeeraj's user avatar
2 votes
1 answer
306 views

Fermionic commutation relation using Jordan-Wigner transformation

How to show in detailed steps that Fermionic annihilation and creation operators under Jordan-Wigner transformation satisfy the Fermionic commutation relation $\{\hat{a}_i,\hat{a}_j\}= \{\hat{a}_i^\...
heromano's user avatar
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4 votes
3 answers
110 views

Why does joint ground state not change under action of beam splitting unitary operator?

How can one show that $\hat{U}|00\rangle=|00\rangle$ where $\hat{U}=e^{-igt(\hat{a}^\dagger_2\hat{a}_1+\hat{a}^\dagger_1\hat{a}_2)}$ and $|00\rangle$ is the unique joint zero eigenstate of the ...
heromano's user avatar
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8 votes
3 answers
383 views

If a Hamiltonian is quadratic in the ladder operator, why is its time evolution linear in the ladder operator?

How can one show that $\hat{U}^\dagger\hat{a}\hat{U}$ (with $\hat{U} =e^{-i\hat{H}t}$) involves only linear orders of the ladder operator, when $H$ is the general quadratic Hamiltonian $(\hat{H} = \...
heromano's user avatar
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4 votes
2 answers
314 views

Fermionic occupation operator and nearest neighbor Fermionic hopping interaction as a qubit operator

How to express Fermionic occupation operator $(\hat{a}_j^\dagger\hat{a}_j)$ and nearest neighbor Fermionic hopping interaction ($H_h= J\sum_{i=1}\hat{a}_i^\dagger \hat{a}_{i+1}+\hat{a}_{i+1}^\dagger \...
heromano's user avatar
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2 votes
2 answers
367 views

Need some help with simulating molecules with VQE

I have studied the example of the simulation of LiH molecule in Learning Quantum Computation using Qiskit. It is available on this link: https://qiskit.org/textbook/ch-applications/vqe-molecules.html#...
Antonio Sannia's user avatar
2 votes
0 answers
217 views

Calculating energy function with 1&2-RDM (reduced density matrix) in Qiskit

I am now working on designing quantum error mitigation with variational quantum eigensolvers (VQE). I need to get the 1&2-RDM from Qiskit, which has already been realized by Openchemist pakages ...
ironmanaudi's user avatar
1 vote
0 answers
100 views

Why Measurement Error Mitigation does not seem to improve the result of VQE?

I try to follow https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/algorithms/03_vqe_simulation_with_noise.ipynb to perform measurement error mitigation for calculating H2 energy with ...
fagd's user avatar
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4 votes
1 answer
480 views

Simulation of a helium molecule using Qskit

I am trying to compute the ground state energy of He-He using VQE. For this purpose I have utilized Qskit and have written the following script: ...
user14660's user avatar
2 votes
1 answer
252 views

No. of bits in 160 qubits computer [duplicate]

I read in a book that (https://hub.packtpub.com/quantum-expert-robert-sutor-explains-the-basics-of-quantum-computing/) 160 qubits (quantum bits) could hold $2^{160} \approx1.46\times 10^{48}$ bits ...
Manu Chadha's user avatar
2 votes
1 answer
187 views

How to improve accuracy of ground energy values from a VQE

Using the Qiskit textbook I have been using a VQE to find the ground state energy of Hydrogen at different interatomic distances on a quantum machine. However, the average energy value I will always ...
LouisL's user avatar
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1 vote
0 answers
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Is there a connection between the definitions of one- and two-particle reduced density matrices?

In quantum chemistry, there are concepts about one-particle reduced density matrix (1-RDM) and similarly, the two-particle reduced density matrix (2-RDM). Generally, for an $n$ particle wavefunction $|...
刘环宇's user avatar
3 votes
4 answers
120 views

Where can I get circuits of interest to quantum chemistry to try and simplify?

I am a computer science undergraduate working on a project in simplifying quantum circuits (using the ZX-calculus). I was hoping to try to simplify some circuits of interest rather than randomly ...
shashvat's user avatar
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2 votes
1 answer
347 views

Why VQE gives an incorrect ground state energy for a chain of 4 hydrogen atoms?

I am a bit hesitant to ask this very specific question, as I feel other people need not benefit from it. But since I have struggled for a while, and I think I should get some help. So I am using VQE ...
fagd's user avatar
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2 votes
1 answer
559 views

How is the Hartree accuracy calculated between the exact and VQE results?

In the Simulating Molecules using VQE section of the Qiskit textbook it states an accuracy of $0.0016$ Hartree between the exact and ...
MShakeG's user avatar
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3 votes
1 answer
207 views

What is the convention of indices for the one and two-body integrals in qiskit

I was able to calculate the one and two-body integrals for the H2 with the following code ...
fagd's user avatar
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9 votes
1 answer
247 views

Impact of ordering Hamiltonian terms for Trotterization

In Trotterization, the typical Hamiltonian considered is: $$ H = \sum_{p, q} h_{pq} a^{\dagger}_p a_q + \sum_{p, q, r, s} a^{\dagger}_p a^{\dagger}_q a_r a_s $$ Which is then converted into a sequence ...
C. Kang's user avatar
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7 votes
1 answer
208 views

What are some current applications of Quantum Computing in drug discovery? Are there any test examples of this?

I am interested in applying the power of Quantum Computing to drug discovery. Although I realize that quantum computing is limited in regards to modeling drug-like compounds and their interactions ...
Rob James's user avatar
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3 votes
1 answer
302 views

VQE jobs do not appear in queue

I am trying to calculate the ground state energy of some simple molecules using 'MolecularGroundStateEnergy' tools in qiskit. When I run the calculations for very small molecules (e.g. H2, HeH+) the ...
Joshua's user avatar
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1 vote
1 answer
228 views

Readout using an NMR spectrum

I'm trying to understand how to read results from an NMR quantum computer. According to Nielsen and Chuang: The principal output is the free induction decay signal $$V(t) = V_0\text{Tr}\left[e^{-...
NNN's user avatar
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