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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Approximate decomposition of general $n$-qubit unitary to universal gate set

The Solovay-Kitaev algorithm claims that any $n$-qubit unitary gate can be decomposed to $O(\log^c(1/\epsilon))$ gates in any given universal gate set, e.g. Clifford+T. However, the number of qubits $...
SUSY's user avatar
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Pennylane Spectral gap for Molecules

Pennylane's dataset has a lot of systems, including Quantum Chemistry molecules. Can I extract the spectral gap of the molecule from the dataset (assuming it contains the number). In the case that ...
Zee's user avatar
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Solving the one-electron integral manually in second quantized form

When I am looking into the Hartree-Fock solution to the many bodies electronic system, I came across the one electron integral, which is defined as: $$h_{pq}=\int{\psi_p^\ast\left(r\right)\left(-\frac{...
ScientiaNatura's user avatar
2 votes
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How to define an energy function, for predicting protein structure in quantum computing? [closed]

Let q denote a particular configuration of the protein in a grid, written in the form where $x_i$ and $y_i$ are the $x$ and $y$ coordinate of the $i$th amino acid. For this configuration, how to ...
Pretty's user avatar
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3 votes
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Updating qiskit.chemistry.core.Hamiltonian to qiskit-nature Framework

I recently saw a piece of code that computes molecular bond energy with respect to bond length. I am trying to update the code to the newer qiskit framework (I'm running qiskit 0.45.1 and ...
ScientiaNatura's user avatar
2 votes
0 answers
20 views

Understanding the Role of Qiskit's VQE Code in Light of Pre-calculated Zero-Point Vibrational Energy in Gaussian Files

In the context of quantum computational chemistry, the Qiskit VQE (Variational Quantum Eigensolver) code is often used to calculate the vibrational energies of molecules, including the zero-point ...
Akash Yadav's user avatar
3 votes
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37 views

Advantage of quantum computers over classical computers in fully modeling interactions between atoms?

I'm trying to better understand the advantage quantum computers offer in terms of their ability to more accurately model chemical reactions. As a way to come to a deeper understanding, my question is: ...
Poe's user avatar
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Help me to find error in finding Cost Function for SSVQE algorithm [closed]

Q: Build SSVQE's cost function using the following observable: $$O=2II−2XX+3YY−3ZZ\,.$$ This cost function should take in parameters as input. Use the included variational form, with reference states $...
Kishore's user avatar
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4 votes
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Difference between Qiskit and Openfermion two body integrals

I am struggling with understanding the differences between OpenFermion and Qiskit libraries when it comes to Molecular Data, two body integrals. For example, I am working with the following ...
Eugen's user avatar
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Subespace Search Variational Quantum Eigensolver (SSVQE) with contraints

I am trying to reproduce this paper: https://arxiv.org/pdf/2211.02302.pdf. However, I am having problems in getting the singlet first excited state (S1). The authors in the paper, they use the SSVQE ...
bjail66's user avatar
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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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1 answer
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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 finding eigenfunctions of complicated Hamiltonians exactly

Currently I am an undergrad in chemistry taking a quantum computing class and I'm looking for a topic for a small project involving literary review of QC articles. I was wondering if quantum computing ...
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
1 vote
1 answer
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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
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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
0 votes
1 answer
216 views

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
2 votes
0 answers
83 views

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
0 votes
1 answer
201 views

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
4 votes
1 answer
143 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
170 views

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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2 votes
2 answers
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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
2 votes
1 answer
246 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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1 answer
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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
510 views

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
505 views

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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1 answer
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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. Can ...
Rag's user avatar
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2 votes
1 answer
980 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
797 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
257 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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1 vote
1 answer
85 views

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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5 votes
1 answer
243 views

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
331 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
  • 155
6 votes
1 answer
368 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
508 views

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
  • 155
1 vote
1 answer
219 views

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
  • 155
0 votes
1 answer
236 views

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
0 votes
0 answers
229 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
485 views

Fermionic commutation relation using Jordan-Wigner transformation

How can one show in detailed steps that Fermionic annihilation and creation operators, under Jordan-Wigner transformation, satisfy the Fermionic commutation relations? The Fermionic commutation ...
heromano's user avatar
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4 votes
3 answers
117 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
458 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
454 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
494 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
343 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
134 views

Why measurement error mitigation does not seem to improve the result of VQE?

I try to follow this to perform measurement error mitigation for calculating H2 energy with VQE. With some modification, I did the calculation on "qasm_simulator" with the noise model built ...
fagd's user avatar
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5 votes
1 answer
653 views

Simulation of a helium molecule using Qiskit

I am trying to compute the ground state energy of He-He using VQE. For this purpose I have utilized Qiskit and have written the following script: ...
user14660's user avatar
2 votes
1 answer
354 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
274 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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