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Increasing the active space is crucial to improve the accuracy of the ground-state energy. What values should I use in order to get the ground state energy that is closer to the experimental value? Note that if you have a chemical intuition about which orbitals you want to include in the active space you can use the decompose function (see here) that allows you to choose the active orbitals. This corresponds to a symmetric active space with active_electrons = 8 and active_orbitals = 8. Currently, PennyLane simulators should be able to handle up to ~ 16 qubits. In order to reduce further the size of your simulation you can decrease the number of active electrons and orbitals. So you would end up with a system of 22 electrons and 19 valence orbitals which still requires significant resources (38 qubits). In your case there are 4 core orbitals populated by 8 core electrons. This is hard due to the size and depth of the variational circuit, and the number of terms in the decomposed Hamiltonian.Ī natural approximation is to neglect the core orbitals (orbitals with deep energies that are typically not important for chemical bonding). This requires 46 qubits to simulate the molecular Hamiltonian. įor a minimal basis set (e.g., “sto-3g”) M=23 On the other hand, the total number of molecular orbitals M determines the number of qubits N_\mathrm = 2 \times M (see this tutorial for more details). In principle, one has to include all the electrons in the molecule. Let me start by clarifying that defining an active space is an approximation to keep the simulation within the computational resources at hand. Is there a right way to calculate the number of active_electrons, active_orbitals, and electrons? Hi you very much for sharing your question and welcome to the Xanadu forum! Is there a right way to calculate the number of active_electrons, active_orbitals, and electrons? If yes, in case of the molecule I am using, what values should I use in order to get the ground state energy that is closer to the experimental value?
#I NUMBER OF ELECTRONS CODE#
I am attempting to find its ground state energy by implementing the code provided as one of Amazon Braket’s examples for Pennylane ( ). I have the above molecule with 7 atoms (1O, 1N, 3H, 2C).