| 查看: 884 | 回复: 3 | |||||
| 当前主题已经存档。 | |||||
hbyi金虫 (小有名气)
|
[交流]
【分享】SCF收敛问题的一些解决办法
|
||||
|
If you have an SCF calculation that failed to converge, which of these tricks should you try first? Here are my suggestions with number one being the first thing I try and etc. 1. Try a different initial guess (using the "guess" keyword in Gaussian). For an open shell system, try converging the closed shell ion of the same molecule then using that as an initial guess for the open shell calculation. Adding electrons may give more reasonable virtual orbitals but as a general rule of thumb cations are easier to converge than anions. 2. Another initial guess method is to first run the calculation with a small basis set then get the initial guess for a larger basis set calculation from the previous wave function. 3. Try level shifting ( "SCF=Vshift" in Gaussian). 4. If the SCF is approaching, but not reaching, the convergence criteria relax or ignore the convergence criteria. This is usually done for geometry optimizations which do not converge at the initial geometry then often converge as they approach the equilibrium geometry. 5. Some programs use reduced accuracy integrals to speed the SCF. Using full integral accuracy may be necessary for systems with diffuse functions, long range interactions or low energy excited states. 6. Try changing the geometry. First slightly shortening a bond length then slightly lengthening a bond length then shifting the conformation a bit. 7. Consider trying a different basis set. 8. Consider doing the calculation at a different level of theory. This isn't always practical, but beyond this point the increased number of iterations may make the computation time as much as using a higher level of theory anyway. 9. Turn off the DIIS extrapolation ( "SCF=NoDIIS" in Gaussian ). You should probably give the calculation more iterations along with this. 10. Give the calculation more SCF iterations ( "SCF(MaxCyc=N)" where N is the number of iterations in Gaussian ). This seldom helps but the next option often uses so many iterations that it's worth a try. 11. Use a forced convergence method. (In Gaussian "SCF=QC" is usually the best but on rare occasions "SCF=DM" will be faster). Don't forget to give the calculation an extra thousand iterations or so. The wave function obtained by these methods should be tested to make sure it is a minimum and not just a stable point ( see the "stable" keyword in Gaussian ). 12. See if the software documentation suggests any other ways to change the DIIS method. You may well have to run hundreds of calculations to get enough experience with this to know what works when and how much to change it by. [ Last edited by cadick on 2009-12-14 at 02:50 ] |
回复此楼» 收录本帖的淘帖专辑推荐
 第一性原理概念及相关内容 | 高斯日常学习总结 |
» 猜你喜欢
［调剂信息］211智能人工感知方向国家青年特聘专家课题组招收调剂研究生
已经有0人回复
-
[调剂信息]211智能人工感知方向国家青年特聘专家课题组招收调剂研究生
已经有0人回复
-
物理学I论文润色/翻译怎么收费?
已经有55人回复
-
0702一志愿吉大B区求调剂 本科期间发表一篇Sci
已经有2人回复
-
070200求调剂，一志愿某211，288分
已经有18人回复
-
法国博士后职位
已经有0人回复
-
重庆交大26年硕士生招生拟调剂通知已出！欢迎加入机器视觉与3D光学成像课题组。
已经有0人回复
-
广州大学光电信息工程专业调剂，招收物理学专业学生
已经有1人回复
-
0702一志愿吉大B区求调剂 本科期间发表一篇Sci
已经有0人回复
我为量化狂
木虫 (初入文坛)
- 应助: 0 (幼儿园)
- 金币: 2597.5
- 散金: 15
- 红花: 1
- 帖子: 48
- 在线: 170.4小时
- 虫号: 629086
- 注册: 2008-10-17
- 性别: GG
- 专业: 理论和计算化学
2楼2009-05-15 11:58:12
awmc2008
至尊木虫 (文坛精英)
学习者
- 应助: 62 (初中生)
- 金币: 13759.6
- 红花: 10
- 帖子: 12279
- 在线: 736.8小时
- 虫号: 600677
- 注册: 2008-09-12
- 性别: GG
- 专业: 凝聚态物性 II ：电子结构
3楼2009-05-15 22:13:03
hbyi
金虫 (小有名气)
- 应助: 0 (幼儿园)
- 金币: 3361.7
- 散金: 120
- 红花: 1
- 帖子: 276
- 在线: 90.9小时
- 虫号: 744573
- 注册: 2009-04-09
- 性别: GG
- 专业: 理论和计算化学
4楼2009-05-31 08:59:56
