应《网络安全法》要求，自2017年10月1日起，未进行实名认证将不得使用互联网跟帖服务。为保障您的帐号能够正常使用，请尽快对帐号进行手机号验证，感谢您的理解与支持！

24小时热门版块排行榜    

小木虫论坛-学术科研互动平台 » 计算模拟区 » 第一性原理 » Siesta&Smeagol&Atk » 投影态密度有负值
31/1返回列表
查看: 1674  |  回复: 2
只看楼主 @他人 存档 新回复提醒 (忽略) 收藏    在APP中查看

futiliu

木虫 (小有名气)

[交流] 投影态密度有负值

本人用smeagol算两电极系统的投影态密度时，某些原子上的PDOS出现负值，请问有人碰到这种情况吗？又如何解释呢？谢谢！
回复此楼

» 收录本帖的淘帖专辑推荐

siesta问题

» 猜你喜欢

» 本主题相关价值贴推荐，对您同样有帮助:

» 抢金币啦！回帖就可以得到:

查看全部散金贴
1楼 2012-02-28 08:38:16
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

zhangguangping

木虫 (著名写手)
★
futiliu(金币+1):谢谢参与
WDD880227(金币+1): 感谢交流提示 2012-02-28 15:35:57
这个是由于基组的不正交性导致的。严格说来，如果投影的时候采用一个已经正交的基组来定义的话，就会避免这个问题，但是那个时候PDOS的物理意义没有现在明确。所以有点“鱼和熊掌不可兼得”。

更加详细的解释，我下面引用如下：

http://www.mail-archive.com/sies ... am.es/msg02951.html

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

Dear Siesta users,

I have a problem understanding the output in a .PDOS output file for my
system.  I am getting negative values in the PDOS for the projection
onto a lot of the basis functions.  Perhaps my understanding is wrong,
but surely this should not be?  According to my understanding the PDOS
onto a specific basis function should have peaks at  the energies
corresponding  to the eigenfunctions to which it contributes.

I restarted the PDOS calculation from the output files of a converged
calculation and used 1 SCF iteration with 50x50x50 Monkhorst Pack grid.

Regards,
Rainer


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

Dear Rainer:

   When you are working with a non-orthogonal basis set,
as is the case in Siesta, neither the PDOS nor the Mulliken
population analysis are positive definite magnitudes.

   The reason is due to the fact that the PDOS is defined
as:

   g_mu(eps) = sum_nu rho_mu,nu S_nu,mu delta(eps-eps_i)

   rho_mu,nu = sum_i C_mu,i C*_nu,i

(i stands for the bands, S stands for the overlap matrix,
and C stands for the coefficients of the wave function)
and the non-diagonal elements of the density matrix
might be negative.

   However, the term in the diagonal IS positive definite,
and it is usually larger than the rest of the terms.
Therefore, when the PDOS is negative the value should be
small in absolute value.

   Hope this helps,

       Javier



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

Dear Javier

Thanks very much for your reply.  This certainly helps me understand
why there can be negative values in the PDOS, at least mathematically.
But these negative values of PDOS are not physically meaningful, right?
So how should I interpret them?  Can one just invert them?   I am
getting negative values that are roughly the same size as the positive
values, so I dont feel comfortable just disregarding them.

Regards,
Rainer
-----------------------------------------

Dear Rainer:

   I do not think you can give any physical meaning
to a large negative Projected Density Of States.

   The problem is rather fundamental.
The solution should come from a redefinition
of the PDOS as the projection over a basis of
orthogonalized orbitals. That would imply
a first transformation from our
non-orthogonal basis set to a orthogonal one
(I guess that you will have to multiply
by the inverse of the overlap matrix somewhere).

    Hope this helps,

        Javier
=================================
赞一下 回复此楼
2楼2012-02-28 14:55:07
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖

泡泡毛毛

新虫 (小有名气)
★
futiliu(金币+1): 谢谢参与
楼主你好，打扰了，我用vasp算的PDOS也出现负值，看到你的帖子进来，但是这个问题没有解决方法吗？只能手动改吗？

发自小木虫Android客户端
赞一下 回复此楼
3楼2016-10-26 21:59:41
已阅   回复此楼   关注TA 给TA发消息 送TA红花 TA的回帖
相关版块跳转 我要订阅楼主 futiliu 的主题更新
31/1返回列表
普通表情 龙 兔 虎 猫 高级回复 (可上传附件)
信息提示
关闭
请填处理意见
关闭