Anisotropic interparticle correlations in the simple cubic lattice of single-domain ferroparticles (SCLF) are studied using both theory and computer simulation. The theory is based on the Helmholtz free energy expansion like classical virial series up to the second virial coefficient. The analytical formula for the Helmholtz free energy is incorporated in a logarithmic form to minimize the effects of series truncation. The new theoretical approach, including discrete summation over lattice nodes coordinates, is compared critically against the classical virial expansion of the Helmholtz free energy for the dipolar hard sphere fluid; the main differences between the Helmholtz free energy of SCLF and dipolar hard sphere fluid are discussed. The theoretical results for the Helmholtz free energy, the magnetization, and the initial magnetic susceptibility of the SCLF are compared against Molecular Dynamic simulation data. In all cases, theoretical predictions using logarithmic form of the Helmholtz free energy are seen to be superior, but they only have an applicability range of the effective dipolar coupling constant ${\lambda }_e<1.5$. For highest values of ${\lambda }_e$, the structural transition of the magnetic dipoles in SCLF is observed in Molecular Dynamic simulation. It has been shown that for ${\lambda }_e\gtrsim 2$, an antiferromagnetic order appears in the system.

使用理论和计算机仿真研究了单域铁粒子（SCLF）的简单立方晶格中的各向异性粒子间相关性。该理论基于亥姆霍兹自由能膨胀，例如经典病毒级数直至第二病毒级系数。亥姆霍兹自由能的分析公式以对数形式并入，以最大程度地减少串联截断的影响。新的理论方法，包括在晶格节点坐标上的离散求和，被严格地与偶极硬球流体的亥姆霍兹自由能的经典病毒式扩展进行了比较。讨论了SCLF的亥姆霍兹自由能和偶极硬球流体之间的主要区别。亥姆霍兹自由能，磁化强度，并且将SCLF的初始磁化率与分子动力学模拟数据进行了比较。在所有情况下，使用对数形式的亥姆霍兹自由能的理论预测被认为是优越的，但它们仅具有有效偶极耦合常数的适用范围。${\lambda }_{Ë}<\mathrm{1个}。5$。对于最高值${\lambda }_{Ë}$在分子动力学模拟中观察到了SCLF中磁偶极子的结构转变。已经表明，对于${\lambda }_{Ë}\gtrsim 2$，系统中会出现反铁磁顺序。