Japan\u2019s Advanced Institute of Science and Technology<\/a>, undertook this problem using an ingenious combination of supercomputer simulations and data science. Their work revealed various crystal structures for hydrogen at low temperatures near 0 K and high pressures.<\/p>\n\u201cFor crystal structures under high pressure, we have been able to generate several candidate patterns using a recent data science method known such as genetic algorithms,\u201d explained Professor Maezono. \u201cBut whether these candidates are truly the phases that survive under high pressure can only be determined by high-resolution simulations\u201d.<\/p>\n
Crystal structures<\/h3>\n Therefore, the team searched for various possible structures that can be formed with two to 70 hydrogen atoms at high pressures of 400 to 600 gigapascals (GPa). The team then utilised a technique called \u2018particle swarm optimisation\u2019 and density functional theory (DFT) calculations to estimate their relative stability using first-principles quantum Monte Carlo method and DFT zero-point energy corrections.<\/p>\n
The search produced 10 possible crystal structures that were previously not found by experiments, including nine molecular crystals and one mixed structure,\u00a0Pbam-<\/em>8 comprising atomic and molecular crystal layers appearing alternatively. However, they found that all the 10 structures showed structural dynamic instabilities. To obtain a stable structure, the team relaxed\u00a0Pbam<\/em>-8 in the direction of instability to form a new dynamically stable structure\u00ad called\u00a0P<\/em>21<\/sub>\/c<\/em>-8.\u00a0\u201cThe new structure is a promising candidate for the solid hydrogen phase realized under high-pressure conditions such as that found deep within the Earth,\u201d\u00a0says Dr. Hongo.<\/p>\nThe results<\/h3>\n The new structure was discovered to be more stable than\u00a0Cmca<\/em>-12, a structure that was previously found to be a valid candidate in the H2<\/sub>-PRE phase, one of the six structural phases identified for solid hydrogen at high pressure (360 to 495 GPa) that is stable at near 0 K. The team then further confirmed their results by comparing the infrared spectrum of the two structures, revealing a similar pattern typically observed for the H2<\/sub>-PRE phase.<\/p>\nWhile this is an interesting discovery, the results are significant, explained Professor Maezono:\u00a0\u201cThe hydrogen crystal problem is one of the most challenging and intractable problems in materials science. Depending on the type of approximation used, the predictions can vary greatly and avoiding approximations is a typical challenge. With our result now verified, we can continue our research on other structure prediction problems, such as that for silicon and magnesium compounds, which have a significant impact on earth and planetary science.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"
Using data science and supercomputer simulations, researchers have identified a potential crystal phase for hydrogen solidified at extreme pressures. Elements in the periodic table can appear in multiple forms. For example, Carbon, can exist as diamond or graphite depending on the environmental conditions at the time of formation. Crystal structures that have been formed in […]<\/p>\n","protected":false},"author":19,"featured_media":17079,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[766,24429],"tags":[763,24413,833],"acf":[],"yoast_head":"\n
Study displays novel crystal structure for hydrogen under high pressure<\/title>\n \n \n \n \n \n \n \n \n \n \n \n \n \n\t \n\t \n\t \n \n \n \n \n \n\t \n\t \n\t \n