The Heisenberg exchange coupling parameter *J* (*H* = −2*J**S*_{i} · *S*_{j}) characterises the isotropic magnetic interaction between unpaired electrons, and it is one of the most important spin Hamiltonian parameters of multi-spin open shell systems. The *J* value is related to the energy difference between high-spin and low-spin states, and thus computing the energies of individual spin states are necessary to obtain the *J* values from quantum chemical calculations. Here, we propose a quantum algorithm, ayesian echange coupling parameter calculator with roken-symmetry wave functions (BxB), which is capable of computing the *J* value directly, without calculating the energies of individual spin states. The BxB algorithm is composed of the quantum simulations of the time evolution of a broken-symmetry wave function under the Hamiltonian with an additional term *j**S*^{2}, the wave function overlap estimation with the SWAP test, and Bayesian optimisation of the parameter *j*. Numerical quantum circuit simulations for H_{2} under a covalent bond dissociation, C, O, Si, NH, OH^{+}, CH_{2}, NF, O_{2}, and triple bond dissociated N_{2} molecule revealed that the BxB can compute the *J* value within 1 kcal mol^{−1} of errors with less computational costs than conventional quantum phase estimation-based approaches.

大学の新着ニュースに掲載されました。https://www.osaka-cu.ac.jp/ja/news/2020/201225