Peng Yun, Zhou Xiaojun, Wang Zhifan, Wang Fan
Institute of Atomic and Molecular Physics, Key Laboratory of High Energy Density Physics and Technology, Ministry of Education, Sichuan University, Chengdu 610065, People's Republic of China.
Department of Physics, Shaanxi University of Science and Technology, Xi'an 710021, People's Republic of China.
J Chem Phys. 2021 Jan 14;154(2):024301. doi: 10.1063/5.0031051.
Multireference character in some small boron clusters could be significant, and a previous all-electron fixed-node diffusion quantum Monte Carlo (FN-DMC) calculation with the single-determinant-Jastrow (SDJ) trial wavefunction shows that the atomization energy (AE) of B is overestimated by about 1.4 eV compared with the coupled cluster method with single, doubles, and perturbative triples [CCSD(T)] results. All-electron FN-DMC calculations and those with the pseudopotential (PP) using SDJ and multi-determinant-Jastrow (MDJ) trial wavefunctions with B3LYP orbitals as well as CC calculations at different levels are carried out on B (n = 1-5, Q = -1, 0, 1) clusters. The obtained FN-DMC energies indicate that the node error of the employed SDJ trial wavefunction in all-electron calculations is different from that with the PP for some clusters. The error of AEs and dissociation energies (DEs) from all-electron FN-DMC calculations is larger than that with the PP when the SDJ trial wavefunction is employed, while errors of CC methods do not depend on whether the PP is used. AEs and DEs of the boron clusters are improved significantly when MDJ trial wavefunctions are used in both all-electron calculations and those with the PP, and their error is similar to that of CCSD(T) compared with CCSDT(Q) results. On the other hand, reasonable adiabatic electron detachment energies (ADEs) and ionization potentials (AIPs) are achieved with FN-DMC using SDJ trial wavefunctions and MDJ is less effective on ADEs and AIPs. Furthermore, the relative energy between two structures of B is predicted reliably with FN-DMC using the SDJ trial wavefunction and the effect of MDJ is negligible, while density functional theory results using different exchange-correlation functionals differ significantly.
一些小硼团簇中的多参考特征可能很显著，先前使用单行列式-贾斯卓（SDJ）试探波函数的全电子固定节点扩散量子蒙特卡罗（FN-DMC）计算表明，与单、双和微扰三重耦合簇方法[CCSD(T)]的结果相比，B的原子化能（AE）被高估了约1.4电子伏特。对B（n = 1 - 5，Q = -1, 0, 1）团簇进行了使用SDJ和多行列式-贾斯卓（MDJ）试探波函数以及不同水平的耦合簇（CC）计算的全电子FN-DMC计算和赝势（PP）计算。所获得的FN-DMC能量表明，对于某些团簇，全电子计算中所采用的SDJ试探波函数的节点误差与使用PP时的节点误差不同。当使用SDJ试探波函数时，全电子FN-DMC计算的AE和解离能（DE）的误差大于使用PP时的误差，而CC方法的误差不取决于是否使用PP。当在全电子计算和使用PP的计算中都使用MDJ试探波函数时，硼团簇的AE和DE有显著改善，与CCSDT(Q)结果相比，其误差与CCSD(T)的误差相似。另一方面，使用SDJ试探波函数的FN-DMC能得到合理的绝热电子脱离能（ADE）和电离势（AIP），而MDJ对ADE和AIP的效果较差。此外，使用SDJ试探波函数的FN-DMC能可靠地预测B两种结构之间的相对能量，MDJ的影响可忽略不计，而使用不同交换关联泛函的密度泛函理论结果差异显著。
