Car、Parrinello首次提出的从头计算分子动力学方法有机地结合了密度泛函理论和分子动力学技术, 是目前计算机模拟实验中最先进最要的方法之一。本文简要地阐述了从头计算分子动力学方法的原理和具体实现, 以及近年来这一方法的发展和重要应用。

The electronic and magnetic properties of Mn doping at either cation sites in the class of Ⅰ-Ⅲ-Ⅵ2 chalcopyrites are studied by first-principles calculation. It is found that Mn doping at the Ⅲ site provides holes and stabilizes the ferromagnetic interaction between neutral Mn defects; the neutral MnoCu also stabilizes the ferromagnetism, although it provides electrons to the conduction band, instead of holes. The ferromagnetic stability is generally weaker when the cation or the anion becomes heavier in these chalcopyrites, i.e., along the sequences CuAlS2→CuGaS2→CuInS2 and CuGaS2→CuGaSe2→CuGaTe2. Interestingly, CuAlO2 in the chalcopyrite structure is predicted to have lower FM energy than CuAlS2 despite its lighter anion and shorter bonds. In general, Ⅲ site substitution gives stabler ferromagnetism than Cu substitution. Thus, the preferred growth conditions are Cu-rich and Ⅲ-poor, which maximize MnⅢ replacement. In n-type samples, when MnⅢ is negatively charged, the antiferromagnetic coupling is preferred. In p-type samples, the ground state of positively charged Mn+Cu is also antiferromagnetism. The main feature of the calculated electronic properties of Mn defect at either Cu or Ⅲ site is explained using a simple picture of dangling bond hybride and crystal-field resonance.

The need for spin-injectors having the same zinc-blende-type crystal structure as conventional semiconductor substrates has created significant interests in theoretical predictions of possible metastable “half-metallic” zinc-blende ferromagnets, which are normally more stable in other structure-types, e.g., NiAs. Such predictions were based in the past on differences △bulk in the total energies of the respective bulk crystal (forms szinc blende and NiAs). We show here that the appropriate criterion is comparing difference △epi(as) in epitaxial total energies. This reveals that even if △bulk is small, still for MnAs, CrSb, CrAs, CrTe, △epi＞0 for all substrate lattice constant as, so the zinc-blende phase is not stabilized. For CrS we find △epi(as)＜0, but the system is antiferromagnetic, thus not half-metallic. Finally, zinc-blende CrSe is predicted to be epitaxially stable for as＞6.2 Å and is half metallic.

Recently reported room-temperature ferromagnetic（FM）semiconductors Cd1-xMnxGeP2 and Zn1-xMnxGeP2 point to a possible important role of Ⅱ-Ⅳ-Ⅴ2 chalcopyrite semiconductors in “spintronic” studies. Here, structural, electronic, and magnetic properties of （i） Mn-doped II-Ge-VI2 (Ⅱ= Zn or Cd and V=P or As）chalcopyrites and（ii）the role of S as impurity in Cd1-xMnxGeP2 are studied by first-principles density functional calculations. We find that the total energy of the antiferromagnetic（AFM）state is lower than the corresponding FM state for all systems with Mn composition x=0.25, 0.50, and 1.0. This prediction is in agreement with a recent experimental finding that Zn1-xMnxGeP2 experiences a FM to AFM transition for T less than 47 K. Furthermore, a possible transition to the half-metallic FM phase is predicted in Cd1-xMnxGeP2 due to the electrons introduced by n-type S doping, which indicates the importance of carriers for FM coupling in magnetic semiconductors. As expected, the total magnetic moment for the FM phase is reduced by one mB with each S substituting P.

The nature and origin of ferromagnetism in magnetic semiconductors is investigated by means of highly precise electronic and magnetic property calculations on MnxGe1-x as a function of the location of Mn sites in a large supercell. Surprisingly, the coupling is not always ferromagnetic (FM), even for large Mn-Mn distances. The exchange interaction between Mn ions oscillates as a function of the distance between them and obeys the Ruderman-Kittel-Kasuya-Yosida analytic formula. The estimated Curie temperature is in good agreement with recent experiments, and the estimated effective magnetic moment is about 1.7 µB/Mn, in excellent agreement with the experimental values, (1.4–1.9) µB/Mn.