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小木虫论坛-学术科研互动平台 » 计算模拟区 » 量子化学 » Gaussian » 【求助】请问如何在优化分子时加入外电场
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hjsjs

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[交流] 【求助】请问如何在优化分子时加入外电场 已有2人参与

想在优化分子时加入外电场进行计算，文献中提到“采用Gaussian98的密度泛函方法B3YLP方法在6一311++G(d，p)基组水平上全电子能量梯度优化计算了在不同外场下乙烯的分子构型"

请问这个外电场怎么设置？文献中使用的外电场为0.001a.u., 0.002a.u.为弱电场，0.01 a.u. 0.02 a.u.为强电场
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1楼 2010-05-30 00:39:35
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hjsjs

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刚才查手册，好像是用Field的关键词进行设置呀
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2楼2010-05-30 00:44:04
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lb1586551

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hjsjs(金币+3): 2010-05-31 03:24:09
Field


The Field keyword requests that a finite field be added to calculation. In Gaussian 03, the field can either involve electric multipoles (through hexadecapoles) or a Fermi contact term. Field requires a parameter in one of these two formats:

M�N or F(M)N

where M designates a multipole, and F(M) designates a Fermi contact perturbation for atom M (following the ordering in the molecule specification section of the input file). N*0.0001 specifies the magnitude of the field in atomic units in the first format, and specifies the magnitude of the Fermi contact perturbation in the second format.

Thus, Field=X+10 applies an electric dipole field in the X direction of 0.001 au, while Field=XXYZ-20 applies the indicated hexadecapole field with magnitude 0.0020 au and direction opposite to the default (which is determined by the standard orientation). Similarly, Field=F(3)27 applies a perturbation of 0.0027 times the spin density on atom 3.

Note that the coefficients are those of the Cartesian operator matrices; be careful of the choice of sign convention when interpreting the results.

All parameters are in the input orientation.

The field specification parameter may be placed among any other options as desired. Archiving is disabled when Field is specified.



Read
Reads the coefficients of 34 electric multipole components from the input stream in free format.

OldRead
Reads the coefficients of 35 electric multipole components from the input stream, in the old style format (including the monopole term): using format 3D20.10 (the first component is a charge).

RWF
Takes the 35 multipole components from the read-write file.

ERWF
Extracts only the three electric dipole field components from the read-write file.

Checkpoint
Reads the 35 multipole components from the checkpoint file. Chk is a synonym for Checkpoint.

EChk
Extracts only the three electric dipole field components from the checkpoint file.



Single point energy, geometry optimizations, and Force and Scan calculations.

LIMITATIONS
Note that if symmetry is left on during a GVB calculation, the finite field will or will not lead to correct numerical derivatives, depending on whether the selected field breaks molecular symmetry. To be safe, use Guess=NoSymm whenever using Field with GVB.



To perform geometry optimizations in the presence of an electric field, you must use Opt=Z-Matrix NoSymm keywords and define the input geometry either in traditional Z-matrix coordinates or symbolic Cartesian coordinates. Here is an example using a Z-matrix:

# RHF/3-21G Field=x+60 Opt=Z-Matrix NoSymm

Z-Matrix optimization

0  1
C
H   1   B1
H   1   B2   2   A1
H   1   B3   2   A2   3   D1
H   1   B4   2   A3   3   D2

  B1            1.070000
  B2            1.070000
  B3            1.070000
  B4            1.070000
  A1          109.471203
  A2          109.471203
  A3          109.471231
  D1          120.000015
  D2         -119.999993
Here is an example using symbolic Cartesian coordinates:

# HF/6-31G(d) Opt=Z-Matrix Field=z-50 NoSymm

Symbolic Cartesian coordinates optimization

0  1
O 0   x1 y1 z1
H 0   x2 y2 z2
H 0   x3 y3 z3

x1=0.0
y1=0.0
z1=0.12
x2=0.0
y2=0.75
z2=-0.46
x3=0.0
y3=-0.75
z3=-0.46
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3楼2010-05-30 09:14:11
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