QMCPACK is an open source quantum Monte Carlo package for ab initio electronic structure calculations. It supports calculations of metallic and insulating solids, molecules, atoms, and some model Hamiltonians. Implemented real space quantum Monte Carlo algorithms include variational, diffusion, and reptation Monte Carlo. QMCPACK uses Slater-Jastrow type trial wavefunctions in conjunction with a sophisticated optimizer capable of optimizing tens of thousands of parameters. The orbital space auxiliary-field quantum Monte Carlo method is also implemented, enabling cross validation between different highly accurate methods. The code is specifically optimized for calculations with large numbers of electrons on the latest high performance computing architectures, including multicore central processing unit and graphical processing unit systems. We detail the program's capabilities, outline its structure, and give examples of its use in current research calculations. The package is available at http://qmcpack.org.

Cathodes of lithium-rich layered oxides for highenergy Li-ion batteries in electrically powered vehicles are attracting considerable attention by the research community. However, current research is insufficient to account for their complex reaction mechanism and application. Here, the structural evolution of lithium−manganese-rich layered oxides at different temperatures during electrochemical cycling has been investigated thoroughly, and their structural stability has been designed. The results indicated structure conversion from the two structures into a core−shell structure with a single distorted-monoclinic LiTMO 2 structure core and disorderedspinel/rock salt structure shell, along with lattice oxygen extraction and lattice densification, transition-metal migration, and aggregation on the crystal surface. The structural conversion behavior was found to be seriously temperature sensitive, accelerated with higher temperature, and can be effectively adjusted by structural design. This study clarifies the structural evolution mechanism of these lithium-rich layered oxides and opens the door to the design of similar high-energy materials with better cycle stability.

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Layered transition-metal oxides have attracted intensive interest for cathode materials of sodium-ion batteries. However, they are hindered by the limited capacity and inferior phase transition due to the gliding of transition-metal layers upon Na+ extraction and insertion in the cathode materials. Here, we report that the large-sized K+ is riveted in the prismatic Na+ sites of P2-Na0.612K0.056MnO2 to enable more thermodynamically favorable Na+ vacancies. The Mn-O bonds are reinforced to reduce phase transition during charge and discharge. 0.901 Na+ per formula are reversibly extracted and inserted, in which only the two-phase transition of P2 ↔ P’2 occurs at low voltages. It exhibits the highest specific capacity of 240.5 mAh g−1 and energy density of 654 Wh kg−1 based on the redox of Mn3+/Mn4+, and a capacity retention of 98.2% after 100 cycles. This investigation will shed lights on the tuneable chemical environments of transition-metal oxides for advanced cathode materials and promote the development of sodium-ion batteries.

Potassium-ion batteries (KIBs) are emerging as one of the most promising candidates for large-scale energy storage owing to the natural abundance of the materials required for their fabrication and the fact that their intercalation mechanism is identical to that of lithium-ion batteries. However, the larger ionic radius of K + is likely to induce larger volume expansion and sluggish kinetics, resulting in low specific capacity and unsatisfactory cycle stability. A new Ni/ Mn-based layered oxide, P2-type K 0.44 Ni 0.22 Mn 0.78 O 2 , is designed and synthesized. A cathode designed using this material delivers a high specific capacity of 125.5 mAh g −1 at 10 mA g −1 , good cycle stability with capacity retention of 67% over 500 cycles and fast kinetic properties. In situ X-ray diffraction recorded for the initial two cycles reveals single solid-solution processes under P2-type framework with small volume change of 1.5%. Moreover, a cathode electrolyte interphase layer is observed on the surface of the electrode after cycling with possible components of K 2 CO 3 , RCO 2 K, KOR, KF, etc. A full cell using K 0.44 Ni 0.22 Mn 0.78 O 2 as the cathode and soft carbon as the anode also exhibits exceptional performance, with capacity retention of 90% over 500 cycles as well as superior rate performance. These findings suggest P2-K 0.44 Ni 0.22 Mn 0.78 O 2 is a promising candidate as a high-performance cathode for KIBs.