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VASP MD 得到 amorphous結(jié)構(gòu) 已有1人參與
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大家好。我想利用VASP跑分子動力學(xué)模擬得到amorphous結(jié)構(gòu)。思路大概是從crystalline phase起先melt再quench。有一個問題是,amorphous phase的密度一般比crystalline phase密度要低,所以其晶格常數(shù)要大一些。如果始終用NVT ensemble的話晶格常數(shù)不會改變,這樣得到的結(jié)構(gòu)不太合理,因?yàn)榈玫降腶morphous 結(jié)構(gòu)密度和crystalline phase一樣,會存在很大 residual stress。所以我試著用NpT ensemble (ISIF=3),保持壓強(qiáng)為一個大氣壓,期望晶格常數(shù)會有所增加,得到合理的結(jié)構(gòu)。現(xiàn)在問題是,NpT MD時候晶格常數(shù)一直不變,請問怎么回事? INCAR file: # General parameters for this run System= SnO2 NCORE = 12 # Electronic specification PREC = Normal ! standard precision, we recomend the use of PREC = Normal ENCUT = 150 ! cutoff should be set manually, smaller if ultra-large supercell ISMEAR= 0 SIGMA = 0.01 LREAL = Auto ! Real space to spped up for large molecular dynamics runs ALGO = Very Fast ! For large molecular dynamics runs NELMIN= 4 ! Set minimum steps of electronic optimization EDIFF = 1E-3 ! Do not use default, too much drift # MD related # NpT ISYM = 0 ! strongly recommened for MD, no symmertry IBRION= 0 ! molecular dynamics NSW = 7500 ! 7500 steps POTIM = 2 ! timestep 2 fs # SMASS = -1 ! Nose Hoover thermostat ISIF = 3 MDALGO= 3 ! TEBEG = 3000 TEEND = 300 ! temperature PSTRESS= 0.001 # Output control NBLOCK= 50 ! XDATCAR updated every 50 steps NWRITE = 0 ! For MD, use NWRITE = 0 or NWRITE = 1 LCHARG = .FALSE. LWAVE = .FALSE. |
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我也是查的manual設(shè)置的。有些參數(shù)不知道怎么設(shè)置就leave it default. NpT要怎么設(shè)置? 1. Set the standard MD-related tags: IBRION=0, TEBEG, POTIM, and NSW. 2. Set ISIF=3 to allow for relaxation of the cell volume and shape. At the moment, dynamics with fixed volume+variable shape (ISIF=4) or fixed shape+variable volume (ISIF=7) are not available. 3. Set MDALGO=3 to invoke the Langevin thermostat. 4. Specify friction coefficients for all species in the POSCAR file, by means of the LANGEVIN_GAMMA-tag. 5. Specify a separate set of friction coefficient for the lattice degrees-of-freedom, using the LANGEVIN_GAMMA_L-tag. 6. Set a mass for the lattice degrees-of-freedom, using the PMASS-tag. 7. Optionally, one may define an external pressure (in kB), by means of the PSTRESS-tag |
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