Abstract
The accurate calculation of molecular energy spectra, a very complicated work, is of importance in many applied fields. Relying on the VQE-UCC algorithm, it is very possible to calculate the molecular energy spectrum on a noisy intermediate scale quantum computer. However, due to the limitation of the number of qubits and coherent time in quantum computers, the complexity of VQE-UCC algorithm still needs to be reduced in the simulation of macromolecules. We develop a new VQE-UCC method to calculate the ground state of the molecule according to the symmetry of the system, the complexity of which is reduced. Using this method we get the ground and excite state of four kinds of molecules. The method and the results are of great significance for the promotion of quantum chemical simulations.
Highlights
In this year, quantum computing has been widely concerned as a new paradigm of computing
One mainly chooses the unitary coupled cluster method (UCC) [8, 9], coming from the classical single reference coupled cluster method (SRCC) [10, 11], which is more suitable for quantum computers
We propose a simpler UCC variant method, the singlet and pair UCC (SPUCC), based on the spin symmetry of molecules
Summary
Quantum computing has been widely concerned as a new paradigm of computing. One mainly chooses the unitary coupled cluster method (UCC) [8, 9], coming from the classical single reference coupled cluster method (SRCC) [10, 11], which is more suitable for quantum computers It divides the electron orbitals into two parts, the occupied orbitals and the unoccupied orbitals. The method can reduce the computational complexity while keeping the computational accuracy Based on this method, we calculate the grounds of molecules with different structures and properties, and get good results as expected. The VQE algorithm uses the quantum computer to prepare quantum states and to get the expected value of Hamiltonian, which are difficult for the classical computer.
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