Hynninen Antti-Pekka, Dijkstra Marjolein
Soft Condensed Matter, Debye Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
Phys Rev E Stat Nonlin Soft Matter Phys. 2005 Nov;72(5 Pt 1):051402. doi: 10.1103/PhysRevE.72.051402. Epub 2005 Nov 30.
We study the phase behavior of hard and soft spheres with a fixed dipole moment using Monte Carlo simulations. The spheres interact via a pair potential that is a sum of a hard-core Yukawa (or screened-Coulomb) repulsion and a dipole-dipole interaction. The system can be used to model colloids in an external electric or magnetic field. Two cases are considered: (i) colloids without charge (or dipolar hard spheres) and (ii) colloids with charge (or dipolar soft spheres). The phase diagram of dipolar hard spheres shows fluid, face-centered-cubic (fcc), hexagonal-close-packed (hcp), and body-centered-tetragonal (bct) phases. The phase diagram of dipolar soft spheres shows, in addition to the above mentioned phases, a body-centered-orthorhombic (bco) phase, and is in agreement with the experimental phase diagram [Nature (London) 421, 513 (2003)]. In both cases, the fluid phase is inhomogeneous but we find no evidence of a gas-liquid phase separation. The validity of the dipole approximation is verified by a multipole moment expansion.
我们使用蒙特卡罗模拟研究了具有固定偶极矩的硬球和软球的相行为。这些球通过一种对势相互作用，该对势是硬核 Yukawa（或屏蔽库仑）排斥与偶极 - 偶极相互作用之和。该系统可用于模拟处于外部电场或磁场中的胶体。考虑了两种情况：（i）不带电的胶体（或偶极硬球）和（ii）带电的胶体（或偶极软球）。偶极硬球的相图显示出流体、面心立方（fcc）、六方密堆积（hcp）和体心四方（bct）相。偶极软球的相图除了上述相之外，还显示出体心正交（bco）相，并且与实验相图一致[《自然（伦敦）》421, 513 (2003)]。在这两种情况下，流体相都是不均匀的，但我们没有发现气 - 液相分离的证据。通过多极矩展开验证了偶极近似的有效性。
