In this project i want to use variational quantum circuit within the variational quantum eigensolver method implemented in qiskit runtime to investigate the potential energy surface (PES) of a water molecule because it is a noncolinear molecule so the bond angle of H-O-H is different than 180. To simulate this process i first create a 3D potential energy surface by varying the the angle and O-H bond distance using the result from exact diagnoalization using Numpy. The optimal angle and bond distance are determined by minimizing the potential energy surface function. Using the predicted optimal bond angles and bond lengths, we used VQE method with a customized ansatz to determine the minimal energy. Using qiskit runtime, the VQE process was run numerous times till the VQE energy is within 4 mHa of the minimal energy obtained from exact diagnolization to determine the optimal angle for the PES calculation using VQE. After the chemical accuracy is satisfied, we calculated the potential energy surface of water by varying the bond angles using VQE with the initial starting angle obtained from the previous VQE run.
The notebook was compiled on the IBMQ environment using the following modules:
qiskit-0.29
qiskit-nature
sckit-learn
qiskit-runtime
matplotlib
numpy
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