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happyzyf銅蟲 (小有名氣)
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[求助]
vasp計算分子動力學(xué)溫度變化不正常 已有1人參與
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各位大俠好!我再用vasp的分子動力學(xué)做一個模擬退火的過程,感覺結(jié)果有問題,OSZICAR里面的溫度是從0開始的。INCAR設(shè)置如下 NPAR = 10 LPLANE = .TRUE. LREAL = AUTO ICHARG = 1 ENCUT = 300 PREC = Normal ALGO = VeryFast NELMIN = 4 NELM = 150 EDIFF = 1E-4 ISMEAR = 0 SIGMA = 0.1 # ISPIN = 2 # LWAVE = .FALSE. # LCHARG = .FALSE. IBRION = 0 NSW = 5000 POTIM = 2 SMASS = 3 TEBEG = 774 TEEND = 300 NBLOCK = 1 OSZICAR中溫度從0開始上升,最高到1400多,然后開始下降,這中間還有震蕩,不知道是什么原因。后來我改了INCAR里面的參數(shù),固定體系始末溫度都在300K,想讓它平衡一段時間看看,設(shè)置如下 NPAR = 10 LPLANE = .TRUE. LREAL = AUTO ICHARG = 1 ENCUT = 300 PREC = Normal ALGO = VeryFast NELMIN = 4 NELM = 150 EDIFF = 1E-4 ISMEAR = 0 # SIGMA = 0.1 # ISPIN = 2 LWAVE = .FALSE. LCHARG = .FALSE. IBRION = 0 NSW = 3000 POTIM = 1 SMASS = 2 TEBEG = 300 TEEND = 300 NBLOCK = 1 KBLOCK = 50 OSZICAR里面溫度仍然是從0開始上升 多謝~ |

銅蟲 (小有名氣)

銅蟲 (小有名氣)

銅蟲 (小有名氣)
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手冊中說“For SMASS>=0 a canonical ensemble is simulated using the algorithm of Nosé. The Nosé mass controls the frequency of the temperature oscillations during the simulation (see [1, 2, 3]. For SMASS=0 Nosé-mass corresponding to period of 40 time steps will be chosen. The Nosé-mass should be set so that the induced temperature fluctuation show approximately the same frequencies as the typical 'phonon'-frequencies for the specific system. For liquids something like 'phonon'-frequencies might be obtained from the spectrum of the velocity auto-correlation function. If the ionic-frequencies differ by an order of magnitude from the frequencies of the induce temperature fluctuations Nosé thermostat and ionic movement might decouple leading to a non canonical ensemble. The frequency of the approximate temperature fluctuations induced by the Nosé-thermostat can be found on the OUTCAR file.”也就是說“SMASS大于等于0時,表示是用用Nose算法來模擬NVT系綜。Nose mass控制了模擬過程中的溫度針紡的頻率。SMASS=0時,默認步長40 time step,需設(shè)置Nose mass使得溫度震蕩頻率與體系聲子頻率一致。對于液體,可以從速度自修正函數(shù)中得到類似聲子的頻率。離子的頻率與聲子頻率差一個數(shù)量級會導(dǎo)致系綜不再是正則系綜。溫度震蕩的近似頻率可以從OUTCAR中得到!钡抢锩嫒匀粵]有區(qū)分SMASS=0,1,2,3的情況。還有一個問題就是OUTCAR里面沒找到手冊里說的溫度震蕩的頻率,麻煩告知一下好嗎?謝謝~ |
金蟲 (正式寫手)

銅蟲 (小有名氣)
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http://www.gaoyang168.com/bbs/viewthread.php?tid=7106381&fpage=1&target=blank http://www.gaoyang168.com/bbs/viewthread.php?tid=7017928&fpage=1&target=blank;樓主這個其實我也是新手一般大家都是先NVT跑一下,然后NVE跑,但是NVT中SMASS選哪個,一般取>0,詳細的話估計的看它的原代碼. |

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