phonopy算的自由能数值在低温下为何为正值？

calvincui · 发表于 Post on 2023-5-17 22:46:24

最近用phonopy的功能phonopy -t mesh.conf -c POSCAR-unitcell得到了结构的自由能，但是发现在低温下结构的自由能为正值。但是同样的结构vasp得到的数值就为负值（F= -.10197374E+04）
看了phonopy计算自由能的公式，感觉它算的就是体系在这个温度下的自由能。但为何跟vasp算的数值有天壤之别。。。。难道是phonopy算的是从0K 到该温度下的δF？但如果是这样的话，在0K下的δF应该为0才对。。。不太明白，请各位大神指教

以下为phonopy算的在不同温度下的自由能数值

# temperature[K] Free energy [kJ/mol] Entropy [J/K/mol] Heat capacity [J/K/mol] Energy [kJ/mol]
   0.0000000    94.8141587    0.0000000    0.0000000    94.8141587
10.0000000    94.8122692    0.5627799    1.1467641    94.8178970
20.0000000    94.7982387    2.5422929    5.8551495    94.8490846
30.0000000    94.7546386    6.5386615    15.2604912    94.9507984
40.0000000    94.6602217    12.6954164    28.7410774    95.1680384
50.0000000    94.4942787    20.7799454    44.5207855    95.5332760
60.0000000    94.2397112    30.3379275    60.7898696    96.0599869
70.0000000    93.8841871    40.8995820    76.5092822    96.7471578
80.0000000    93.4196197    52.0953194    91.3628405    97.5872453
90.0000000    92.8410122    63.6747533 105.4170257    98.5717400
100.0000000    92.1453741    75.4813520 118.8469473    99.6935093
110.0000000    91.3309503    87.4195104 131.7997326 100.9470964
120.0000000    90.3967492    99.4286435 144.3552368 102.3281864
130.0000000    89.3422822 111.4666601 156.5335082 103.8329480
140.0000000    88.1674295 123.5007959 168.3165139 105.4575409
150.0000000    86.8723726 135.5031361 179.6688688 107.1978430
160.0000000    85.4575561 147.4487463 190.5526178 109.0493555
170.0000000    83.9236621 159.3150810 200.9358885 111.0072259
180.0000000    82.2715864 171.0819145 210.7968582 113.0663310
190.0000000    80.5024152 182.7314186 220.1246778 115.2213847
200.0000000    78.6174007 194.2482178 228.9186716 117.4670443
210.0000000    76.6179366 205.6193700 237.1867264 119.7980043
220.0000000    74.5055344 216.8342698 244.9434319 122.2090738
230.0000000    72.2818004 227.8844901 252.2082883 124.6952331
240.0000000    69.9484152 238.7635863 259.0041307 127.2516759
250.0000000    67.5071148 249.4668812 265.3558262 129.8738351
260.0000000    64.9596741 259.9912461 271.2892413 132.5573981
270.0000000    62.3078924 270.3348897 276.8304557 135.2983126
280.0000000    59.5535810 280.4971595 282.0051824 138.0927857
290.0000000    56.6985529 290.4783621 286.8383583 140.9372779
300.0000000    53.7446137 300.2796013 291.3538676 143.8284941
310.0000000    50.6935549 309.9026358 295.5743690 146.7633720
320.0000000    47.5471474 319.3497561 299.5211998 149.7390694
330.0000000    44.3071372 328.6236769 303.2143384 152.7529506
340.0000000    40.9752411 337.7274460 306.6724066 155.8025727
350.0000000    37.5531444 346.6643671 309.9127017 158.8856729
360.0000000    34.0424983 355.4379337 312.9512474 162.0001544
370.0000000    30.4449182 364.0517748 315.8028570 165.1440749
380.0000000    26.7619828 372.5096087 318.4812043 168.3156341
390.0000000    22.9952335 380.8152053 320.9988965 171.5131636
400.0000000    19.1461736 388.9723546 323.3675487 174.7351154
410.0000000    15.2162686 396.9848412 325.5978568 177.9800535
420.0000000    11.2069464 404.8564235 327.6996673 181.2466443
430.0000000    7.1195974 412.5908171 329.6820447 184.5336488
440.0000000    2.9555752 420.1916814 331.5533340 187.8399150
450.0000000    -1.2838031 427.6626088 333.3212196 191.1643709
460.0000000    -5.5972556 435.0071173 334.9927800 194.5060184
470.0000000    -9.9835355 442.2286440 336.5745384 197.8639272
480.0000000 -14.4414298 449.3305409 338.0725094 201.2372298
490.0000000 -18.9697585 456.3160716 339.4922415 204.6251166
500.0000000 -23.5673739 463.1884098 340.8388565 208.0268310
510.0000000 -28.2331596 469.9506382 342.1170854 211.4416659
520.0000000 -32.9660296 476.6057480 343.3313014 214.8689594
530.0000000 -37.7649272 483.1566400 344.4855496 218.3080920
540.0000000 -42.6288244 489.6061248 345.5835745 221.7584830
550.0000000 -47.5567208 495.9569244 346.6288448 225.2195876
560.0000000 -52.5476427 502.2116741 347.6245765 228.6908948
570.0000000 -57.6006426 508.3729239 348.5737533 232.1719240

sobereva · 发表于 Post on 2023-10-15 16:03:24

calvincui 发表于 2023-10-15 10:38
也就是把这一列换算成eV然后加到VASP算出的能量上就是这个温度下的自由能数值是吗？

我不用VASP，对单位不清楚
把单位弄统一，加上去就是

calvincui · 发表于 Post on 2023-10-15 10:38:49

sobereva 发表于 2023-5-18 00:08
Phonopy给你的是自由能热校正量，加到电子能量上才是自由能

也就是把这一列换算成eV然后加到VASP算出的能量上就是这个温度下的自由能数值是吗？

sobereva · 发表于 Post on 2023-5-18 00:08:21

Phonopy给你的是自由能热校正量，加到电子能量上才是自由能

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