CHEN Lei (1983-), male, doctor, associate professor, major in high pressure materials and structures. E-mail: stonley@163.com
The crystal structure prediction of K2N2 in the pressure range of 0–150 GPa using an advanced particle swarm crystal structure search method was conducted. The results show that the stable ground state phase of K2N2 is a monoclinic C2/m structure, and three high-pressure structures including Na2N2-type, Cmmm, and C2/c are identified at pressures of 1.7, 3.6, 122 GPa, respectively. The volume dependence on pressure shows that the three phase transitions, i. e., C2/m→Na2N2-type, Na2N2-type→Cmmm, and Cmmm→C2/c, are all first order phase transitions, corresponding to volume collapses of 14.4%, 22.5%, and 4.0%, respectively. During the high pressure phase transitions of K2N2, the coordination number of K atom increases from 5 to 10, and a change in the nature of the N-N bonding from N=N dimmer in the ground state of C2/m structure to N―N single bond chain in the high-pressure C2/c phase is accompanied. The high-pressure C2/c phase exhibits semiconducting properties with a band gap of 2.0 eV, while C2/m, Na2N2-type, and Cmmm phases have metallic behaviors. Electronic structure calculation and electron-localized function analysis indicate that the high-pressure structural phase transition of K2N2 is due to the K-p lone-pair electrons activation and their participation in bonding with N atoms under high pressure.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |