Szabó P Bernát, Csóka József, Kállay Mihály, Nagy Péter R
Department of Physical Chemistry and Materials Science, Faculty of Chemical Technology and Biotechnology, Budapest University of Technology and Economics, Műegyetem rkp. 3, H-1111 Budapest, Hungary.
HUN-REN-BME Quantum Chemistry Research Group, Műegyetem rkp. 3, H-1111 Budapest, Hungary.
J Chem Theory Comput. 2023 Nov 28;19(22):8166-8188. doi: 10.1021/acs.jctc.3c00881. Epub 2023 Nov 3.
The extension of the highly optimized local natural orbital (LNO) coupled cluster (CC) with single-, double-, and perturbative triple excitations [LNO-CCSD(T)] method is presented for high-spin open-shell molecules based on restricted open-shell references. The techniques enabling the outstanding efficiency of the closed-shell LNO-CCSD(T) variant are adopted, including the iteration- and redundancy-free second-order Møller-Plesset and (T) formulations as well as the integral-direct, memory- and disk use-economic, and OpenMP-parallel algorithms. For large molecules, the efficiency of our open-shell LNO-CCSD(T) method approaches that of its closed-shell parent method due to the application of restricted orbital sets for demanding integral transformations and a novel approximation for higher-order long-range spin-polarization effects. The accuracy of open-shell LNO-CCSD(T) is extensively tested for radicals and reactions thereof, ionization processes, as well as spin-state splittings, and transition-metal compounds. At the size range where the canonical CCSD(T) reference is accessible (up to 20-30 atoms), the average open-shell LNO-CCSD(T) correlation energies are found to be 99.9 to 99.95% accurate, which translates into average absolute deviations of a few tenths of kcal/mol in the investigated energy differences already with the default settings. For more extensive molecules, the local errors may grow, but they can be estimated and decreased via affordable systematic convergence studies. This enables the accurate modeling of large systems with complex electronic structures, as illustrated on open-shell organic radicals and transition-metal complexes of up to 179 atoms as well as on challenging biochemical systems, including up to 601 atoms and 11,000 basis functions. While the protein models involve difficulties for local approximations, such as the spin states of a bounded iron ion or an extremely delocalized singly occupied orbital, the corresponding single-node LNO-CCSD(T) computations were feasible in a matter of days with 10s to 100 GB of memory use. Therefore, the new LNO-CCSD(T) implementation enables highly accurate computations for open-shell systems of unprecedented size and complexity with widely accessible hardware.
基于受限开壳层参考,提出了一种用于高自旋开壳层分子的高度优化的局域自然轨道(LNO)耦合簇(CC)方法,该方法包含单、双和微扰三重激发[LNO-CCSD(T)]。采用了能使闭壳层LNO-CCSD(T)变体具有卓越效率的技术,包括无迭代和冗余的二阶莫勒-普列斯特定理和(T)公式,以及积分直接、节省内存和磁盘使用且支持OpenMP并行的算法。对于大分子,由于在要求较高的积分变换中应用了受限轨道集以及对高阶长程自旋极化效应采用了新的近似方法,我们的开壳层LNO-CCSD(T)方法的效率接近其闭壳层母方法。开壳层LNO-CCSD(T)的准确性在自由基及其反应、电离过程、自旋态分裂以及过渡金属化合物方面进行了广泛测试。在可达规范CCSD(T)参考的尺寸范围内(多达20 - 30个原子),发现平均开壳层LNO-CCSD(T)相关能的准确度为99.9%至99.95%,这在默认设置下,对于所研究的能量差而言,转化为平均绝对偏差为十分之几kcal/mol。对于更大的分子,局部误差可能会增大,但可以通过经济实惠的系统收敛研究进行估计并减小。这使得能够对具有复杂电子结构的大系统进行精确建模,如多达179个原子的开壳层有机自由基和过渡金属配合物,以及具有挑战性的生化系统,包括多达601个原子和11000个基函数的系统。虽然蛋白质模型在局部近似方面存在困难,如束缚铁离子的自旋态或极其离域的单占据轨道,但相应的单节点LNO-CCSD(T)计算在使用10s到100GB内存的情况下,只需几天时间就可行。因此,新的LNO-CCSD(T)实现方式能够利用广泛可用的硬件,对前所未有的尺寸和复杂度的开壳层系统进行高精度计算。