题记： “一切错误，皆有原因”。成熟的商业软件如VASP背后都有完备的理论体系做支撑，出现计算结果与实验或文献值不符的情况，一般应从参数的设置及结果数据的提取等方面找原因，不要轻易怀疑软件有bug。

1. 画焓差图时能量的选择

（1） H=E+PV，画焓差图时应选择H，不能选择E，如下面OUTCAR中红色标注部分所示

vi OUTCAR

………

FREE ENERGIE OF THE ION-ELECTRON SYSTEM(eV)

---------------------------------------------------

free  energy   TOTEN =        -3.52331080 eV  (E)

energy  without entropy=       -3.52291615  energy(sigma->0) =       -3.52317925

enthalpy is  TOTEN   =       35.79101554 eV (H)   P V=      39.31432634

dForce = 0.0000000E+00[ 0.000E+00, 0.000E+00]  d Energy = 0.9492035E-05-0.949E-05

dForce = 0.0000000E+00[ 0.000E+00, 0.000E+00]  d Ewald = 0.1695458E+00-0.170E+00

.....

（2）脚本如下-改自wh,注意焓一定要选择“enthalpy is  TOTEN”

#!/bin/sh

rm -f pv_et.txt

for F in 0 10 50 100 150 200 225 230 240 250 265 280 300 350 400 450 500 800 1000 1200 1500 1800  2000 2500 3000 3500 4000 4500 4750 5000 5250 5500 6000

do

cd $F

for file in OUTCAR_*

do

pre=$(awk '/external pressure/{ print $4+$9 }' $file |tail -n 1)

vol=$(awk '/volume of cell/{print $5}' $file |tail -n 1)

et=$(awk '/enthalpy is  TOTEN/{print $5}' $file |tail -n 1)

echo $pre \ \  $vol \ \  $et >> ../vv_et.txt

done

cd ../

done

cat vv_et.txt|sort  -n -k 1 >pv_et.txt

rm vv_et.txt

a=$(awk '{print NR}' pv_et.txt)

echo $a

exit

（3）原脚本is Nice for extracting enthalpy, don't modify any parameters if you don't know what it means.

#!/bin/sh

### wh.2007-11-26 ###

rm -f p_en.txt

for file in OUTCAR_*

do

pre=$(awk '/external pressure/{ print $4+$9 }' $file |tail -n 1)

ent=$(awk '$3=="TOTEN"{print $5}' $file |tail -n 1)

echo $pre $ent \ \ $file >> pp_en.txt

done

cat pp_en.txt|sort -n -k 1 > p_en.txt

rm pp_en.txt

a=$(awk '{print NR}' p_en.txt)

echo $a

exit

2. VASP各能量项的含义 (待补充)

1） 以下为Yanchao Wang 文章摘录

    As is known that Gibbs free energy reduces to H = U + PVat 0 K,(G=H+TS, H=U+PV) where U, Pand V are the static energy, pressure and volume per formula unit,respectively.

    The high pressure competition between U and PVdominate the phase transitions. Although, the first order transi-tions of Pbca→I-42d→P21 have rather small 1.8% and 1.9%volume drops, respectively, these volume reductions are critical to initiate the phase transitions.

   It is calculated thatalthough P2₁structure is 0.59 eV per H₂O unit higher in U than I-42d structure at 17 Mbar, its PV term is 0.62 eV lower owing to the volumereduction associated with a higher packing efficiency.

Energetically, the tuning effect of PV termwith respect to static energy U is substan-tial in light of volumereduction preferable for denser structural packing.

3. 赝势文件中各参数的含义 (待补充)

PAW_PBE H 15Jun2001

1.00000000000000000

parameters from PSCTR are:

  VRHFIN =H: ultrasoft test

  LEXCH  = PE

  EATOM  =    12.4884 eV,     .9179 Ry

  TITEL  = PAW_PBE H 15Jun2001

  LULTRA =        F    use ultrasoft PP ?

  IUNSCR =        0    unscreen: 0-lin 1-nonlin 2-no

  RPACOR =     .000    partial core radius

  POMASS =    1.000; ZVAL   =    1.000    mass and valenz

  RCORE  =    1.100    outmost cutoff radius

  RWIGS  =     .700; RWIGS  =     .370    wigner-seitz radius (au A)

  ENMAX  =  250.000; ENMIN  =  200.000 eV

  RCLOC  =     .701    cutoff for local pot

  LCOR   =        T    correct aug charges

  LPAW   =        T    paw PP

  EAUG   =  400.000

  RMAX   =    2.174    core radius for proj-oper

  RAUG   =    1.200    factor for augmentation sphere

  RDEP   =    1.112    radius for radial grids

  QCUT   =   -5.749; QGAM   =   11.498    optimization parameters

  Description

    l     E      TYP  RCUT    TYP  RCUT

    0   .000     23  1.100

    0   .500     23  1.100

    1  -.300     23  1.100

  Error from kinetic energy argument (eV)

  NDATA  =      100

  STEP   =   20.000   1.050

 5.77      5.50      5.37      5.11      4.99      4.75      4.52      4.40

 4.19      3.98      3.88      3.68      3.49      3.31      3.14      2.98

 2.83      2.68      2.54      2.35      2.22      2.11      1.94      1.84

 1.74      1.61      1.48      1.40      1.29      1.19      1.09      1.01

 .925      .851      .782      .719      .642      .590      .526      .482

 .430      .382      .339      .301      .267      .236      .209      .178

 .157      .133      .113      .988E-01  .832E-01  .697E-01  .562E-01  .467E-01

 .386E-01  .305E-01  .239E-01  .186E-01  .143E-01  .109E-01  .820E-02  .580E-02

 .425E-02  .291E-02  .195E-02  .130E-02  .808E-03  .544E-03  .368E-03  .278E-03

 .239E-03  .227E-03  .225E-03  .224E-03  .218E-03  .204E-03  .181E-03  .156E-03

 .127E-03  .983E-04  .735E-04  .520E-04  .369E-04  .274E-04  .225E-04  .204E-04

 .201E-04  .200E-04  .193E-04  .178E-04  .151E-04  .121E-04  .914E-05  .676E-05

 .512E-05  .437E-05  .412E-05  .410E-05

END of PSCTR-controll parameters