Choosing pseudopotentials
Several pseudopotential variants labeled by suffixes exist for many elements. When making a choice, it is necessary to balance computational cost, accuracy, and transferability.
- To set up a minimal working example of your calculation, follow prepare a POTCAR.
- Try to create a smaller test calculation and perform your own tests to confirm if the quantity of interest is sensitive to the choice of the pseudopotential. It might be possible to opt for a computationally cheaper POTCAR and gain performance. On the other hand, it could be necessary to opt for a computationally demanding setup to obtain correct results.
- With the aspects described in the next section in mind, carefully look over the recommendations for each group in the periodic table.
Aspects to refine the choice of pseudopotentials
Aspect 1: The bond lengths and the valency of the ions.
- Short bonds will require harder potentials, and semicore states might have to be treated as valence for certain chemical bonding. For some elements, variants for specific valency exist; for example, the suffix _2 or _3 can be used to describe fixed divalent or trivalent Lanthanides.
Aspect 2: The physical or chemical property of interest.
- If you are only interested in a rough structure optimization, soft potentials (_s) with minimal valency may suffice. This approach might also work for phonon calculations that rely on large supercells.
- On the other hand, when optimizing a magnetic structure, it may be necessary to include semicore states in the valence (_pv and _sv).
- For the computation of optical properties, it is crucial to use GW potentials.
Aspect 3: The method or algorithm used in your calculation.
- For any calculation involving unoccupied states significantly above the Fermi energy, the _GW variants of potentials are superior and should be used. Particularly, all kinds of calculations within many-body perturbation theory need a high number of empty bands. Therefore, when GW, BSE, etc. is performed, the GW potentials should be used throughout the workflow.
- Hartree-Fock and hybrid caluclations should not be performed with soft potentials (_s). Moreover, any calculations where you switch the exchange-correlation functional should not be performed with soft potentials (_s).
- For standard DFT-ground-state calculations, using _GW or _h potentials is usually unnecessary unless, e.g., the property of interest or geometry of the structure demands it.
Recommendations and advice
Recommended PAW potentials
- The table directly below highlights recommended PAW potentials in bold.
- These potentials are not ideal for calculations involving a large number of excited states as needed, e.g., for optical properties or many-body perturbation theory.
Standard PBE potentials (potpaw.64) Potential name Number of valence electrons Valence electron configuration ENAMX [eV] H 1 1s1 250.0 H.25 0.25 1s0.25 250.0 H.33 0.33 1s0.33 250.0 H.42 0.42 1s0.42 250.0 H.5 0.5 1s0.5 250.0 H.58 0.58 1s0.58 250.0 H.66 0.66 1s0.66 250.0 H.75 0.75 1s0.75 250.0 H1.25 1.25 1s1.25 250.0 H1.33 1.33 1s1.33 250.0 H1.5 1.5 1s1.5 250.0 H1.66 1.66 1s1.66 250.0 H1.75 1.75 1s1.75 250.0 H_AE 1 1s1 1000.0 H_h 1 1s1 700.0 H_s 1 1s1 200.0 He 2 1s2 478.896 He_AE 2 1s2 2135.871 Li 1 2s1 140.0 Li_sv 3 1s2 2s1 499.034 Be 2 2s1.99 2p0.01 247.543 Be_sv 4 1s2 2s1.99 2p0.01 308.768 B 3 2s2 2p1 318.614 B_h 3 2s2 2p1 700.0 B_s 3 2s2 2p1 269.245 C 4 2s2 2p2 400.0 C_h 4 2s2 2p2 741.689 C_s 4 2s2 2p2 273.911 N 5 2s2 2p3 400.0 N_h 5 2s2 2p3 755.582 N_s 5 2s2 2p3 279.692 O 6 2s2 2p4 400.0 O_h 6 2s2 2p4 765.519 O_s 6 2s2 2p4 282.853 F 7 2s2 2p5 400.0 F_h 7 2s2 2p5 772.626 F_s 7 2s2 2p5 289.837 Ne 8 2s2 2p6 343.606 Na 1 3s1 101.968 Na_pv 7 2p6 3s1 259.561 Na_sv 9 2s2 2p6 3s1 645.64 Mg 2 3s2 200.0 Mg_pv 8 2p6 3s2 403.929 Mg_sv 10 2s2 2p6 3s2 495.223 Al 3 3s2 3p1 240.3 Si 4 3s2 3p2 245.345 P 5 3s2 3p3 255.04 P_h 5 3s2 3p3 390.202 S 6 3s2 3p4 258.689 S_h 6 3s2 3p4 402.436 Cl 7 3s2 3p5 262.472 Cl_h 7 3s2 3p5 409.136 Ar 8 3s2 3p6 266.408 K_pv 7 3p6 4s1 116.731 K_sv 9 3s2 3p6 4s1 259.264 Ca_pv 8 3p6 4s2 119.559 Ca_sv 10 3s2 3p6 4s2 266.622 Sc 3 3d2 4s1 154.763 Sc_sv 11 3s2 3p6 3d2 4s1 222.66 Ti 4 3d3 4s1 178.33 Ti_pv 10 3p6 3d3 4s1 222.335 Ti_sv 12 3s2 3p6 3d3 4s1 274.61 V 5 3d4 4s1 192.543 V_pv 11 3p6 3d4 4s1 263.673 V_sv 13 3s2 3p6 3d4 4s1 263.673 Cr 6 3d5 4s1 227.08 Cr_pv 12 3p6 3d5 4s1 265.681 Cr_sv 14 3s2 3p6 3d5 4s1 395.471 Mn 7 3d6 4s1 269.864 Mn_pv 13 3p6 3d6 4s1 269.864 Mn_sv 15 3s2 3p6 3d6 4s1 387.187 Fe 8 3d7 4s1 267.882 Fe_pv 14 3p6 3d7 4s1 293.238 Fe_sv 16 3s2 3p6 3d7 4s1 390.558 Co 9 3d8 4s1 267.968 Co_pv 15 3p6 3d8 4s1 271.042 Co_sv 17 3s2 3p6 3d8 4s1 390.362 Ni 10 3d9 4s1 269.532 Ni_pv 16 3p6 3d9 4s1 367.986 Cu 11 3d10 4s1 295.446 Cu_pv 17 3p6 3d10 4s1 368.648 Zn 12 3d10 4s2 276.723 Ga 3 4s2 4p1 134.678 Ga_d 13 3d10 4s2 4p1 282.691 Ga_h 13 3d10 4s2 4p1 404.601 Ge 4 4s2 4p2 173.807 Ge_d 14 3d10 4s2 4p2 310.294 Ge_h 14 3d10 4s2 4p2 410.425 As 5 4s2 4p3 208.702 As_d 15 3d10 4s2 4p3 288.651 Se 6 4s2 4p4 211.555 Br 7 4s2 4p5 216.285 Kr 8 4s2 4p6 185.331 Rb_pv 7 4p6 4d0.001 5s0.999 121.882 Rb_sv 9 4s2 4p6 4d0.001 5s0.999 220.112 Sr_sv 10 4s2 4p6 4d0.001 5s1.999 229.353 Y_sv 11 4s2 4p6 4d2 5s1 202.626 Zr_sv 12 4s2 4p6 4d3 5s1 229.898 Nb_pv 11 4p6 4d4 5s1 208.608 Nb_sv 13 4s2 4p6 4d4 5s1 293.235 Mo 6 4d5 5s1 224.584 Mo_pv 12 4p6 4d5 5s1 224.584 Mo_sv 14 4s2 4p6 4d5 5s1 242.676 Tc 7 4d6 5s1 228.694 Tc_pv 13 4p6 4d6 5s1 263.523 Tc_sv 15 4s2 4p6 4d6 5s1 318.703 Ru 8 4d7 5s1 213.271 Ru_pv 14 4p6 4d7 5s1 240.049 Ru_sv 16 4s2 4p6 4d7 5s1 318.855 Rh 9 4d8 5s1 228.996 Rh_pv 15 4p6 4d8 5s1 247.408 Pd 10 4d9 5s1 250.925 Pd_pv 16 4p6 4d9 5s1 250.925 Ag 11 4d10 5s1 249.844 Ag_pv 17 4p6 4d10 5s1 297.865 Cd 12 4d10 5s2 274.336 In 3 5s2 5p1 95.934 In_d 13 4d10 5s2 5p1 239.211 Sn 4 5s2 5p2 103.236 Sn_d 14 4d10 5s2 5p2 241.083 Sb 5 5s2 5p3 172.069 Te 6 5s2 5p4 174.982 I 7 5s2 5p5 175.647 Xe 8 5s2 5p6 153.118 Cs_sv 9 5s2 5p6 6s1 220.318 Ba_sv 10 5s2 5p6 5d0.01 6s1.99 187.181 La 11 4f0.0001 5s2 5p6 5d0.9999 6s2 219.292 La_s 9 5p6 5d1 6s2 136.53 Ce 12 4f1 5s2 5p6 5d1 6s2 273.042 Ce_3 11 5s2 5p6 5d1 6s2 176.506 Ce_h 12 4f1 5s2 5p6 5d1 6s2 299.9 Pr 13 4f2.5 5s2 5p6 5d0.5 6s2 337.25 Pr_3 11 5s2 5p6 5d1 6s2 181.719 Pr_h 13 4f2.5 5s2 5p6 5d0.5 6s2 400.742 Nd 14 4f3.5 5s2 5p6 5d0.5 6s2 338.34 Nd_3 11 5s2 5p6 5d1 6s2 182.619 Nd_h 14 4f3.5 5s2 5p6 5d0.5 6s2 402.016 Pm 15 4f4.5 5s2 5p6 5d0.5 6s2 340.358 Pm_3 11 5s2 5p6 5d1 6s2 176.959 Pm_h 15 4f4.5 5s2 5p6 5d0.5 6s2 404.406 Sm 16 4f5.5 5s2 5p6 5d0.5 6s2 341.177 Sm_3 11 5s2 5p6 5d1 6s2 177.087 Sm_h 16 4f5.5 5s2 5p6 5d0.5 6s2 405.382 Eu 17 4f6.5 5s2 5p6 5d0.5 6s2 344.705 Eu_2 8 5p6 6s2 99.328 Eu_3 9 5p6 5d1 6s2 129.057 Eu_h 17 4f6.5 5s2 5p6 5d0.5 6s2 403.212 Gd 18 4f7.5 5s2 5p6 5d0.5 6s2 342.859 Gd_3 9 5p6 5d1 6s2 154.332 Gd_h 18 4f7.5 5s2 5p6 5d0.5 6s2 407.403 Tb 19 4f8.5 5s2 5p6 5d0.5 6s2 340.855 Tb_3 9 5p6 5d1 6s2 155.613 Tb_h 19 4f8.5 5s2 5p6 5d0.5 6s2 405.043 Dy 20 4f9.5 5s2 5p6 5d0.5 6s2 341.547 Dy_3 9 5p6 5d1 6s2 155.713 Dy_h 20 4f9.5 5s2 5p6 5d0.5 6s2 405.886 Ho 21 4f10.5 5s2 5p6 5d0.5 6s2 343.845 Ho_3 9 5p6 5d1 6s2 154.137 Ho_h 21 4f10.5 5s2 5p6 5d0.5 6s2 415.91 Er 22 4f11.5 5s2 5p6 5d0.5 6s2 346.295 Er_2 8 5p6 6s2 119.75 Er_3 9 5p6 5d1 6s2 155.037 Er_h 22 4f11.5 5s2 5p6 5d0.5 6s2 429.583 Tm 23 4f12.5 5s2 5p6 5d0.5 6s2 344.206 Tm_3 9 5p6 5d1 6s2 149.221 Tm_h 23 4f12.5 5s2 5p6 5d0.5 6s2 419.812 Yb 24 4f13.5 5s2 5p6 5d0.5 6s2 344.312 Yb_2 8 5p6 6s2 112.578 Yb_3 9 5p6 5d1 6s2 188.359 Yb_h 24 4f13.5 5s2 5p6 5d0.5 6s2 409.285 Lu 25 4f14 5s2 5p6 5d1 6s2 255.695 Lu_3 9 5p6 5d1 6s2 154.992 Hf 4 5d3 6s1 220.334 Hf_pv 10 5p6 5d3 6s1 220.334 Hf_sv 12 5s2 5p6 5d4 237.444 Ta 5 5d4 6s1 223.667 Ta_pv 11 5p6 5d4 6s1 223.667 W 6 5d5 6s1 223.057 W_sv 14 5s2 5p6 5d5 6s1 223.057 Re 7 5d6 6s1 226.216 Re_pv 13 5p6 5d6 6s1 226.216 Os 8 5d7 6s1 228.022 Os_pv 14 5p6 5d7 6s1 228.022 Ir 9 5d8 6s1 210.864 Pt 10 5d9 6s1 230.283 Pt_pv 16 5p6 5d9 6s1 294.607 Au 11 5d10 6s1 229.943 Hg 12 5d10 6s2 233.204 Tl 3 6s2 6p1 90.14 Tl_d 13 5d10 6s2 6p1 237.053 Pb 4 6s2 6p2 97.973 Pb_d 14 5d10 6s2 6p2 237.835 Bi 5 6s2 6p3 105.037 Bi_d 15 5d10 6s2 6p3 242.839 Po 6 6s2 6p4 159.707 Po_d 16 5d10 6s2 6p4 264.565 At 7 6s2 6p5 161.43 Rn 8 6s2 6p6 151.497 Fr_sv 9 6s2 6p6 7s1 214.54 Ra_sv 10 6s2 6p6 7s2 237.367 Ac 11 6s2 6p6 6d1 7s2 172.351 Th 12 5f1 6s2 6p6 6d1 7s2 247.306 Th_s 10 5f1 6p6 6d1 7s2 169.363 Pa 13 5f1 6s2 6p6 6d2 7s2 252.193 Pa_s 11 5f1 6p6 6d2 7s2 193.466 U 14 5f2 6s2 6p6 6d2 7s2 252.502 U_s 14 5f2 6s2 6p6 6d2 7s2 209.23 Np 15 5f3 6s2 6p6 6d2 7s2 254.26 Np_s 15 5f3 6s2 6p6 6d2 7s2 207.713 Pu 16 5f4 6s2 6p6 6d2 7s2 254.353 Pu_s 16 5f4 6s2 6p6 6d2 7s2 207.83 Am 17 5f5 6s2 6p6 6d2 7s2 255.875 Cm 18 5f6 6s2 6p6 6d2 7s2 257.953 Cf 20 5f8 6s2 6p6 6d2 7s2 414.614
- The following table highlights recommended PAW potentials for calculations involving many states above the Fermi energy in bold.
- They are optimized for scattering properties high above the Fermi level and thus have advantages if many unoccupied states are involved, as for optical properties or many-body perturbation theory. Some results indicate that these GW potentials are also more accurate for ground-state-DFT calculations[1], but the results should be very comparable with the standard potentials in most cases. Unless the uttermost accuracy is required, it is usually not worth paying the extra computational cost required[2] for the GW potentials compared to their standard counterparts.
GW potentials (potpaw.64) Potential name Number of valence electrons Valence electron configuration ENAMX [eV] H_GW 1 1s1 300.0 H_GW_new 1 1s1 536.615 H_h_GW 1 1s1 700.0 He_GW 2 1s2 405.78 Li_AE_GW 3 1s2 2p1 433.699 Li_GW 1 2s1 112.104 Li_sv_GW 3 1s2 2p1 433.699 Be_GW 2 2s1.9999 2p0.001 247.543 Be_sv_GW 4 1s2 2p2 537.454 B_GW 3 2s2 2p1 318.614 B_GW_new 3 2s2 2p1 318.614 B_h_GW 3 2s2 2p1 731.373 C_GW 4 2s2 2p2 413.992 C_GW_new 4 2s2 2p2 433.983 C_h_GW 4 2s2 2p2 741.689 C_s_GW 4 2s2 2p2 304.843 N_GW 5 2s2 2p3 420.902 N_GW_new 5 2s2 2p3 452.633 N_h_GW 5 2s2 2p3 755.582 N_s_GW 5 2s2 2p3 312.986 O_GW 6 2s2 2p4 414.635 O_GW_new 6 2s2 2p4 466.797 O_h_GW 6 2s2 2p4 765.519 O_s_GW 6 2s2 2p4 334.664 F_GW 7 2s2 2p5 487.698 F_GW_new 7 2s2 2p5 480.281 F_h_GW 7 2s2 2p5 848.626 Ne_GW 8 2s2 2p6 432.275 Ne_s_GW 8 2s2 2p6 318.26 Na_sv_GW 9 2s2 2p6 3p1 372.853 Mg_GW 2 3s2 126.143 Mg_pv_GW 8 2p6 3s2 403.929 Mg_sv_GW 10 2s2 2p6 3d2 429.893 Al_GW 3 3s2 3p1 240.3 Al_sv_GW 11 2s2 2p6 3s2 3p1 411.109 Si_GW 4 3s2 3p2 245.345 Si_sv_GW 12 2s2 2p6 3s2 3p2 547.578 P_GW 5 3s2 3p3 255.04 S_GW 6 3s2 3p4 258.689 Cl_GW 7 3s2 3p5 262.472 Ar_GW 8 3s2 3p6 290.599 K_sv_GW 9 3s2 3p6 3d1 248.998 Ca_sv_GW 10 3s2 3p6 3d2 281.43 Sc_sv_GW 11 3s2 3p6 3d3 378.961 Ti_sv_GW 12 3s2 3p6 3d4 383.774 V_sv_GW 13 3s2 3p6 3d5 382.321 Cr_sv_GW 14 3s2 3p6 3d6 384.932 Mn_GW 7 3d6 4s1 278.466 Mn_sv_GW 15 3s2 3p6 3d7 384.627 Fe_GW 8 3d7 4s1 321.007 Fe_sv_GW 16 3s2 3p6 3d8 387.837 Co_GW 9 3d8 4s1 323.4 Co_sv_GW 17 3s2 3p6 3d9 387.491 Ni_GW 10 3d9 4s1 357.323 Ni_sv_GW 18 3s2 3p6 3d10 389.645 Cu_GW 11 3d10 4s1 417.039 Cu_sv_GW 19 3s2 3p6 3d10 4s1 467.331 Zn_GW 12 3d10 4s2 328.191 Zn_sv_GW 20 3s2 3p6 3d10 4s2 401.665 Ga_GW 3 4s2 4p1 134.678 Ga_d_GW 13 3d10 4s2 4p1 404.602 Ga_sv_GW 21 3s2 3p6 3d10 4s2 4p1 404.602 Ge_GW 4 4s2 4p2 173.807 Ge_d_GW 14 3d10 4s2 4p2 375.434 Ge_sv_GW 22 3s2 3p6 3d10 4s2 4p2 410.425 As_GW 5 4s2 4p3 208.702 As_sv_GW 23 3s2 3p6 3d10 4s2 4p3 415.313 Se_GW 6 4s2 4p4 211.555 Se_sv_GW 24 3s2 3p6 3d10 4s2 4p4 469.344 Br_GW 7 4s2 4p5 216.285 Br_sv_GW 25 3s2 3p6 3d10 4s2 4p5 475.692 Kr_GW 8 4s2 4p6 252.232 Rb_sv_GW 9 4s2 4p6 4d1 221.197 Sr_sv_GW 10 4s2 4p6 4d2 224.817 Y_sv_GW 11 4s2 4p6 4d3 339.758 Zr_sv_GW 12 4s2 4p6 4d4 346.364 Nb_sv_GW 13 4s2 4p6 4d5 353.872 Mo_sv_GW 14 4s2 4p6 4d6 344.914 Tc_sv_GW 15 4s2 4p6 4d7 351.044 Ru_sv_GW 16 4s2 4p6 4d8 348.106 Rh_GW 9 4d8 5s1 247.408 Rh_sv_GW 17 4s2 4p6 4d9 351.206 Pd_GW 10 4d9 5s1 250.925 Pd_sv_GW 18 4s2 4p6 4d10 356.093 Ag_GW 11 4d10 5s1 249.844 Ag_sv_GW 19 4s2 4p6 4d11 354.43 Cd_GW 12 4d10 5s2 254.045 Cd_sv_GW 20 4s2 4p6 4d10 5s2 361.806 In_d_GW 13 4d10 5s2 5p1 278.624 In_sv_GW 21 4s2 4p6 4d10 5s2 5p1 366.771 Sn_d_GW 14 4d10 5s2 5p2 260.066 Sn_sv_GW 22 4s2 4p6 4d10 5s2 5p2 368.778 Sb_GW 5 5s2 5p3 172.069 Sb_d_GW 15 4d10 5s2 5p3 263.1 Sb_sv_GW 23 4s2 4p6 4d10 5s2 5p3 372.491 Te_GW 6 5s2 5p4 174.982 Te_sv_GW 24 4s2 4p6 4d10 5s2 5p4 376.618 I_GW 7 5s2 5p5 175.647 I_sv_GW 25 4s2 4p6 4d10 5s2 5p5 381.674 Xe_GW 8 5s2 5p6 179.547 Xe_sv_GW 26 4s2 4p6 4d10 5s2 5p6 400.476 Cs_sv_GW 9 5s2 5p6 5d1 198.101 Ba_sv_GW 10 5s2 5p6 5d1 6s1 267.02 La_GW 11 4f0.2 5s2 5p6 5d0.8 6s2 313.688 Ce_GW 12 4f1 5s2 5p6 5d1 6s2 304.625 Hf_sv_GW 12 5s2 5p6 5d4 309.037 Ta_sv_GW 13 5s2 5p6 5d5 286.008 W_sv_GW 14 5s2 5p6 5d6 317.132 Re_sv_GW 15 5s2 5p6 5d7 317.012 Os_sv_GW 16 5s2 5p6 5d8 319.773 Ir_sv_GW 17 5s2 5p6 5d9 319.843 Pt_GW 10 5d9 6s1 248.716 Pt_sv_GW 18 5s2 5p6 5d10 323.669 Au_GW 11 5d10 6s1 248.344 Au_sv_GW 19 5s2 5p6 5d11 306.658 Hg_sv_GW 20 5s2 5p6 5d10 6s2 312.028 Tl_d_GW 15 5s2 5d10 6s2 6p1 237.053 Tl_sv_GW 21 5s2 5p6 5d10 6s2 6p1 316.583 Pb_d_GW 16 5s2 5d10 6s2 6p2 237.809 Pb_sv_GW 22 5s2 5p6 5d10 6s2 6p2 317.193 Bi_GW 5 6s2 6p3 146.53 Bi_d_GW 17 5s2 5d10 6s2 6p3 261.876 Bi_sv_GW 23 5s2 5p6 5d10 6s2 6p3 323.513 Po_d_GW 18 5s2 5d10 6s2 6p4 267.847 Po_sv_GW 24 5s2 5p6 5d10 6s2 6p4 326.618 At_d_GW 17 5d10 6s2 6p5 266.251 At_sv_GW 25 5s2 5p6 5d10 6s2 6p5 328.529 Rn_d_GW 18 5d10 6s2 6p6 267.347 Rn_sv_GW 26 5s2 5p6 5d10 6s2 6p6 329.758
Selecting a pseudopotential set
- Generally, we recommend using the latest release of pseudopotentials.
Tip: For compatibility reasons or to accurately reproduce another calculation, you might need to use another (older) pseudopotential release. Consult the list of available pseudopotentials.
Hydrogen-like atoms with fractional valence
- Twelve hydrogen-like potentials are supplied for a valency between 0.25 and 1.75. Further potentials might become available, c.f. available pseudopotentials. These are useful, e.g., to passivate dangling surface bonds.
Mind: The POTCAR files restrict the number of digits for the valency (typically 2, at most 3 digits). Therefor, using three H.33 potentials does yield 0.99 electrons and not 1.00 electron. This can cause undesirable hole- or electron-like states. Set the NELECT tag in the INCAR file to correct the total number of electrons.
First-row elements
- For the 1st row elements B, C, N, O, and F, three potential versions exist, the plain one, a hard version, and a soft version. For most purposes, the standard version of PAW potentials is most appropriate. They yield reliable results for energy cutoffs between 325 and 400 eV, where 370-400 eV are required to predict vibrational properties accurately. Binding geometries and energy differences are already well reproduced at 325 eV. The typical bond-length errors for first row dimers (N2, CO, O2) are about 1% compared to more accurate DFT calculations. The hard pseudopotentials (_h) give results that are essentially identical to the best DFT calculations presently available (FLAPW, or Gaussian with very large basis sets). The soft potentials (_s) are optimized to work around 250-280 eV. They yield reliable description for most oxides, such as VxOy, TiO2, CeO2, but fail to describe some structural details in zeolites, i.e., cell parameters, and volume.
- For Hartree-Fock (HF) and hybrid-functional calculations, we strictly recommend using the standard, standard GW, or hard potentials. For instance, the O_s potential can cause unacceptably large errors even in transition metal oxides. Generally, the soft potentials are less transferable from one exchange-correlation functional to another and often fail when the exact exchange needs to be calculated.
Tip: If dimers with short bonds are present in the system (H2O, O2, CO, N2, F2, P2, S2, Cl2), we recommend using the _h potentials. Specifically, C_h, O_h, N_h, F_h, P_h, S_h, Cl_h, or their _GW counterparts. Otherwise, the standard version is often the best choice for first-row elements.
Alkali and alkali-earth elements (simple metals)
- For Li (and Be), a standard potential and a potential that treats the 1s shell as valence states are available (Li_sv, Be_sv). One should use the _sv potentials for many applications since their transferability is much higher than the standard potentials.
- For the other alkali and alkali-earth elements, the semi-core s and p states should be treated as valence states as well. For lighter elements (Na-Ca), it is usually sufficient to treat the 2p and 3p states as valence states (_pv), respectively. For Rb-Sr, the 4s, 4p, and 5s, 5p states, must be treated as valence states (_sv).
Tip: For alkali and alkali-earth metals, the _sv variants should be chosen, other than for very light elements Na, Mg, K, and Ca, where _pv is usually sufficient.
p-elements
- For Ga, Ge, In, Sn, Tl-At, the lower-lying d states should be treated as valence states (_d potential). For these elements, alternative potentials that treat the d states as core states are also available but should be used with great care.
d-elements
- For the d elements, applies the same as for the alkali and earth-alkali metals: the semi-core p states and possibly the semi-core s states should be treated as valence states. In most cases, however, reliable results can be obtained even if the semi-core states are kept frozen.
- When to switch from X_pv potentials to the X potentials depends on the required accuracy and the row for the 3d elements, even the Ti, V, and Cr potentials give reasonable results but should be used with uttermost care. 4d elements are the most problematic, and we advise using the X_pv potentials up to Tc_pv. For 5d elements the 5p states are rather strongly localized (below 3 Ry), since the 4f shell becomes filled. One can use the standard potentials starting from Hf, but we recommend performing test calculations. For some elements, X_sv potentials are available (,e.g., Nb_sv, Mo_sv, Hf_sv). These potentials usually have very similar energy cutoffs as the _pv potentials and can also be used. For HF-type and hybrid-functional calculations, we strongly recommend using the _sv and _pv potentials whenever possible.
Tip: As a rule of thumb the p states should be treated as valence states for d-elements, if their eigenenergy lies above 3 Ry.
f-elements
- Due to self-interaction errors, f electrons are not handled well by the presently available density functionals. In particular, partially filled f states are often incorrectly described. For instance, all f states are pinned at the Fermi-level, leading to large overbinding for Pr-Eu and Tb-Yb. The errors are largest at quarter and three-quarter filling, e.g., Gd is handled reasonably well since 7 electrons occupy the majority f shell. These errors are DFT and not VASP related.
- Particularly problematic is the description of the transition from an itinerant (band-like) behavior observed at the beginning of each period to localized states towards the end of the period. For the 4f elements, this transition occurs already in La and Ce, whereas the transition sets in for Pu and Am for the 5f elements. A routine way to cope with the inabilities of present DFT functionals to describe the localized 4f electrons is to place the 4f electrons in the core. Such potentials are available and described below; however, they are expected to fail to describe magnetic properties arising f orbitals. Furthermore, PAW potentials in which the f states are treated as valence states are available, but these potentials are expected to fail to describe electronic properties when f electrons are localized. In this case, one might treat electronic correlation effects more carefully, e.g., by employing hybrid functionals or introducing on-site Coulomb interaction.
- For some elements, soft versions (_s) are available as well. The semi-core p states are always treated as valence states, whereas the semi-core s states are treated as valence states only in the standard potentials. For most applications (oxides, sulfides), the standard version should be used since the soft versions might result in s ghost-states close to the Fermi-level (,e.g., Ce_s in ceria). The soft versions are, however, expected to be sufficiently accurate for calculations on intermetallic compounds.
Lanthanides with fixed valence
- In addition, special GGA potentials are supplied for Ce-Lu, in which f electrons are kept frozen in the core, which is an attempt to treat the localized nature of f electrons. The number of f electrons in the core equals the total number of valence electrons minus the formal valency. For instance, according to the periodic table, Sm has a total of 8 valence electrons, i.e., 6 f electrons and 2 s electrons. In most compounds, Sm adopts a valency of 3; hence 5 f electrons are placed in the core when the pseudopotential is generated. The corresponding potential can be found in the directory Sm_3. The formal valency n is indicted by _n, where n is either 3 or 2. Ce_3 is, for instance, a Ce potential for trivalent Ce (for tetravalent Ce, the standard potential should be used).
Warning: f-elements are notoriously hard to describe with DFT due to self-interaction errors in the strongly localized orbitals. Placing some, or all, 4f electrons in the core can rectify this issue, but then the description of magnetism will fail and transferability will suffer.
Tip: If you are not interested in 4f-magnetism, and know the valency of your lanthanide, use the _2 or _3 potentials.
Test your setup
- Even if you have taken a lot of care to optimize your pseudopotential choice, it is always good to perform some test calculations with other potentials, if necessary on a small prototype system. You might realize that you need extra accuracy, or that you are leaving performance on the table by using unnecessarily hard POTCARs for your problem.
Related tags and sections
POTCAR, Prepare a POTCAR, Available pseudopotentials
Theoretical background: Pseudopotentials, Projector-augmented-wave formalism
References
- ↑ Emanuele Bosoni, Louis Beal, Marnik Bercx, Peter Blaha, Stefan Blügel, Jens Bröder, Martin Callsen, Stefaan Cottenier, Augustin Degomme, Vladimir Dikan, Kristjan Eimre, Espen Flage-Larsen, Marco Fornari, Alberto Garcia, Luigi Genovese, Matteo Giantomassi, Sebastiaan P. Huber, Henning Janssen, Georg Kastlunger, Matthias Krack, Georg Kresse, Thomas D. Kühne, Kurt Lejaeghere, Georg K. H. Madsen, Martijn Marsman, Nicola Marzari, Gregor Michalicek, Hossein Mirhosseini, Tiziano M. A. Müller, Guido Petretto, Chris J. Pickard, Samuel Poncé, Gian-Marco Rignanese, Oleg Rubel, Thomas Ruh, Michael Sluydts, Danny E. P. Vanpoucke, Sudarshan Vijay, Michael Wolloch, Daniel Wortmann, Aliaksandr V. Yakutovich, Jusong Yu, Austin Zadoks, Bonan Zhu, Giovanni Pizzi, How to verify the precision of density-functional-theory implementations via reproducible and universal workflows, Nat Rev Phys 6, 45–58 (2024).
- ↑ For the potpaw_PBE.64 potential set, ENMAX is on average ~26 eV (~11%) and EAUG ~210 eV (~42%) larger for the GW potentials compared to their standard counterparts with the same valency.