12楼: Originally posted by 姚海峰456 at 2012-08-01 21:42:17
已经用第一性原理优化好的单胞，用gulp计算声子谱会出现虚频，怎么解决？——求大神帮忙啊！！！

13楼: Originally posted by gemucai at 2012-08-02 18:56:11
我记得gulp是经典的紧束缚方法吧？朝出现虚频的方向改变原子位置试试。...

GULP is a program for performing a variety of types of simulation on materials using boundary conditions of 0-D (molecules and clusters), 1-D (polymers), 2-D (surfaces, slabs and grain boundaries), or 3-D (periodic solids). The focus of the code is on analytical solutions, through the use of lattice dynamics, where possible, rather than on molecular dynamics. A variety of force fields can be used within GULP spanning the shell model for ionic materials, molecular mechanics for organic systems, the embedded atom model for metals and the reactive REBO potential for hydrocarbons. Analytic derivatives are included up to at least second order for most force fields, and to third order for many.

3楼: Originally posted by gemucai at 2012-05-25 18:59:36
问题解决了。

跟大家分享一下我的解决方法，以后碰到有虚频的情况不妨增加smearing的宽度，即degauss的大小，效果很灵的。其实有时候根本不需要过度地优化，我优化到0.0000001ry/bohr也有很大虚频，但是degauss增 ...

14楼: Originally posted by souledge at 2012-08-02 20:39:39
GULP是紧束缚么……我怎么记得GULP是类似于经典的分子动力学的东西呢……记得实验室的人用这货跑上千个原子的分子动力学，也就一天的事～还是在一台三年前的四核电脑上……不过，至于他参数是不是足够收敛，我就不 ...

16楼: Originally posted by gemucai at 2012-08-03 09:12:12
问得非常好，这是一个我没搞清楚的问题。我曾经保持k点不变，改变展宽，结果是不收敛的。有大虾说一般是先定展宽，再增加k点达到收敛。当然对于我这个绝缘体系，fixed就足够了，但我也很想知道对于导体而言，展宽为 ...