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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3 votes
1 answer
279 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 ...
1 vote
0 answers
39 views

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 ...
0 votes
0 answers
27 views

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{...
2 votes
0 answers
36 views

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 ...
3 votes
0 answers
43 views

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 ...
2 votes
1 answer
242 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&...
3 votes
1 answer
345 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 ...
2 votes
0 answers
19 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 ...
1 vote
0 answers
133 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 ...
1 vote
0 answers
150 views

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 $|...
2 votes
0 answers
93 views

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 ...
2 votes
0 answers
76 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 ...
1 vote
0 answers
34 views

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 ...
1 vote
0 answers
48 views

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 ...
3 votes
0 answers
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: ...
5 votes
1 answer
623 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: ...
0 votes
1 answer
195 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 ...
1 vote
0 answers
58 views

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 $...
2 votes
1 answer
462 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 ...
4 votes
0 answers
51 views

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 ...
0 votes
1 answer
109 views

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, ...
1 vote
1 answer
90 views

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 $$ \...
0 votes
1 answer
229 views

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....
1 vote
1 answer
97 views

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” ...
2 votes
1 answer
203 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?
6 votes
1 answer
102 views

Do we know anything about the computational complexity of the exchange-correlation functional?

Density functional theory is based on the Hohenberg-Kohn (HK) theorems and aims to compute the ground-state many-body wavefunction of a physical material and/or molecules. To put it simply, the HK ...
4 votes
2 answers
429 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 \...
0 votes
1 answer
182 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 ...
4 votes
1 answer
137 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 ...
3 votes
1 answer
165 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} \...
2 votes
1 answer
261 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 ...
2 votes
2 answers
831 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 ...
4 votes
1 answer
489 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 ...
1 vote
1 answer
159 views

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 ...
1 vote
1 answer
93 views

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 ...
3 votes
1 answer
487 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 ...
4 votes
2 answers
317 views

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

I am running a VQEUCCFactory for H2 on a real hardware device. ...
2 votes
2 answers
484 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#...
8 votes
1 answer
2k views

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}...
2 votes
1 answer
916 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 ...
5 votes
1 answer
765 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 ...
0 votes
0 answers
228 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 ...
2 votes
1 answer
248 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 ...
5 votes
1 answer
232 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 ...
1 vote
1 answer
84 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 ...
6 votes
1 answer
358 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 ...
2 votes
1 answer
494 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=...
1 vote
1 answer
198 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: ...
0 votes
1 answer
224 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 ...
7 votes
1 answer
265 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 ...