Chemistry Reference

In-Depth Information

β

U
M
V
MM
V
MXM
V
2

BCDW

M
2+
M
4+

X
2+
M
2+

X

−3

|y|

1.5

2

2

4

CDW

M
2+
M
2+
X
3+
M
3+

X

−
|y|

1

2.5

2

4

|y|

β

ACP

M
2+
M
3+
X
3+
M
2+

X

−
|y|

12 .54

CP

M
2+
M
3+

X

M
2+
M
3+

X

−

|y|

122 5

Fig. 12.5 Schematic structures of the electronic phases and the coefficients of their partial

energies per binuclear unit with respect to site-diagonal electron-lattice coupling

, on-site

repulsion
U
M
, nearest-neighbor repulsion
V
MM
,
V
MXM
, and next-nearest-neighbor repulsion
V
2
,

in the strong-coupling limit

b

12.6 Site-Diagonal Versus Site-Off-Diagonal Electron-Lattice

Interactions

The ACP phase is found at low temperatures in Pt
2
(RCS
2
)
4
I(R

CH
3
,
n
-C
4
H
9
)

[
10
,
11
], where the MMX chains are neutral. There is no counterion that acts as an

obstacle to displacements of M ions as in R
4
[Pt
2
(pop)
4
I]
n
H
2
O. Then, we set
K
MXM

to be zero. To start with, we simply ignore the long-range interactions and study the

competition between the site-diagonal (

¼

) electron-lattice

couplings and the effect of the on-site repulsion
U
M
on it. The site-off-diagonal

coupling

b

) and site-off-diagonal (

a

stabilizes the ACP phase, where the binuclear units are dimerized. It is

regarded as a spin-Peierls state because a singlet is formed on the nearest-neighbor

M sites accompanied with an X site in-between. Exactly diagonalizing the present

a

Search WWH ::

Custom Search