xtb version 6.8.0

This release combines new features with extensive bug fixes and numerical consistency improvements. As a result, xtb 6.8.0 introduces small changes to calculated energies compared to previous releases. Differences in absolute total energies can reach the millihartree range, particularly for large systems, while the impact on relative energies is generally negligible. Compared to xtb 6.7.1, the WTMAD2 on GMTKN55 changes by less than 0.0002 kcal/mol for GFN0–GFN2. The 1,988-atom nylon complex from LNCI16 shows a total-energy change of approximately 0.0013 Hartree with GFN2-xTB, while its binding energy changes by only 0.041 kcal/mol.

The native xtb and tblite implementations are now fully consistent (< 1e-10 Eh deviations), preparing the complete transition to tblite in the next releases.

Many thanks to Alberto Boldrini (@AlbertoBoldrini), Ty Balduf (@TyBalduf), M. Chandler Bennett (@mcbennet), James H. Brown (@james-qbraid), Robin Dahl (@robin-dahl), Sebastian Ehlert (@awvwgk), Ikko Eltociear Ashimine (@eltociear), Thomas Froitzheim (@thfroitzheim), Marvin Friede (@marvinfriede), Igor Gerasimov (@foxtran), Johannes Gorges (@gorges97), Albert Katbashev (@Albkat), Sreekanth Kunchapu (@sreekanth221998), Rasmus Sloth Lundkvist (@rasmusslothlundkvist), Niels Maeder (@nmaeder), Marcel Müller (@marcelmbn), Christoph Plett (@cplett), Felix Pultar (@pultar), Thomas Rose (@Thomas3R), Tim Schramm (@tkschramm), Leopold Seidler (@lmseidler), Christian Selzer (@chselz), Yoel Sevi (@g8j39), Philip Turner (@philipturner), SY Wang (@Growl1234), Daniel Wiczew (@DanielWicz), Lukas Wittmann (@lukaswittmann), and Shan Yu (@shaneraphel) for contributing to this release.

What's Changed

• Extended tblite integration: Support for solvation (ddCOSMO, ddCPCM, ddPCM), electric fields, localized orbitals, docking, ONIOM, and periodic GFN1/GFN2 calculations, together with improved SCF algorithms and solvation models.
  PRs: #1072, #1081, #1085, #1160, #1219, #1225, #1327, #1393, #1397, #1404, #1405, #1408, #1433, #1454, #1458, #1459, #1460, #1461, #1463, #1473, #1474, #1475, #1476, #1477, #1478, #1491, #1502, #1507, #1508, #1509
• Hessians and vibrational analysis: Implementation of the O1NumHess algorithm, reusable internal-coordinate infrastructure, and improvements to Hessian calculations, vibrational analysis, and thermochemistry.
  PRs: #1004, #1175, #1176, #1177, #1188, #1236, #1237, #1316, #1381, #1421, #1423, #1426, #1427, #1429, #1432, #1435, #1446, #1481, #1489, #1492, #1500
• GFN-FF: Reparameterization for lanthanides, extension to actinides, and improvements to topology handling, numerical stability, and performance.
  PRs: #1103, #1105, #1201, #1202, #1204, #1222, #1287, #1288, #1289, #1350, #1362, #1425, #1428, #1437, #1438, #1450, #1467, #1494
• CEH: Implementation of CEH gradients and improved thread safety.
  PRs: #1153, #1217
• ONIOM: Support for tblite Hamiltonians and improved handling of constraints and fixed atoms in ONIOM calculations.
  PRs: #1461, #1471
• Docking: Extended docking support with tblite Hamiltonians and improvements to aISS, geometry optimization, and constraint handling.
  PRs: #1089, #1173, #1187, #1194, #1198, #1460, #1498
• Molecular dynamics and constraints: Improved restart handling, input validation, random seed control, and constraint algorithms, including SHAKE and minimum hopping.
  PRs: #1218, #1424, #1431, #1436, #1455, #1457
• C-API: Added solvent-model selection and Hessian access, along with improved resource handling.
  PRs: #1068, #1071, #1434
• Performance optimizations and bug fixes: Faster SCF calculations, gradients, and molecular integrals, reduced memory usage, improved OpenMP parallelization, and numerous numerical stability and reliability fixes.
  PRs: #721, #1051, #1125, #1140, #1166, #1167, #1168, #1170, #1171, #1178, #1179, #1183, #1186, #1189, #1190, #1191, #1192, #1193, #1196, #1208, #1214, #1223, #1229, #1231, #1232, #1234, #1235, #1242, #1248, #1253, #1255, #1268, #1272, #1275, #1278, #1281, #1292, #1298, #1299, #1309, #1331, #1356, #1357, #1358, #1360, #1361, #1363, #1366, #1368, #1406, #1441, #1444, #1449, #1456, #1464, #1465, #1466, #1479, #1483, #1490, #1493, #1495, #1501
• Build system and documentation: Updated dependencies, expanded compiler and platform support, improved CMake and Meson builds, static release binaries, and updated documentation and references.
  PRs: #1060, #1077, #1087, #1088, #1093, #1102, #1106, #1121, #1128, #1133, #1139, #1165, #1180, #1181, #1184, #1206, #1207, #1215, #1243, #1244, #1260, #1263, #1276, #1282, #1300, #1324, #1344, #1348, #1351, #1354, #1374, #1383, #1398, #1413, #1452, #1462, #1480, #1482, #1484, #1496, #1497, #1499, #1503, #1510, #1511, #1512, #1513, #1514

New Contributors

• @james-qbraid made their first contribution in #1051
• @dependabot[bot] made their first contribution in #1093
• @marvinfriede made their first contribution in #1202
• @thfroitzheim made their first contribution in #1214
• @lukaswittmann made their first contribution in #1217
• @rasmusslothlundkvist made their first contribution in #1218
• @eltociear made their first contribution in #1263
• @lmseidler made their first contribution in #1309
• @AlbertoBoldrini made their first contribution in #1316
• @nmaeder made their first contribution in #1348
• @chselz made their first contribution in #1356
• @DanielWicz made their first contribution in #1360
• @Growl1234 made their first contribution in #1408
• @sreekanth221998 made their first contribution in #1444
• @mcbennet made their first contribution in #1441
• @shaneraphel made their first contribution in #1450
• @robin-dahl made their first contribution in #1463
• @g8j39 made their first contribution in #1466
• @philipturner made their first contribution in #1467
• @tkschramm made their first contribution in #1492

Full Changelog: v6.7.1...v6.8.0