Chemistry Reference
In-Depth Information
deuterium D
2
[
124
,
125
], melted carbon, graphite or diamond C [
126
-
130
], melted
aluminum chloride AlCl
3
[
131
], and liquid phosphorus P [
132
], were examined.
Liquid metals and alloys
were investigated as well from AIMD because of their
importance in physics, chemistry, industry, electronics, and engineering. These
studies contain Li [
133
], Na [
134
], Al-Si alloy [
135
], Si [
136
,
137
], K-Pb [
138
],
Fe-Si [
139
], Ni [
140
], Cu [
141
], GaAs [
142
], Ge [
143
-
145
], As
2
Se
3
[
146
], Se [
147
],
Zr [
148
], CdTe [
142
], CsPb [
149
], and Hg [
150
]. For a review see the article by
Kresse [
151
].
4.2.3 Properties of Mixtures and Solvent Effects
In the following section examples of solvated molecules, ions, and ionic liquids in
water as well as in methanol are given. Both the effects of the solvent on the solute
as well as the opposite effects of the dissolved species on the solvent were
considered. In many studies these effects are reflected in altered dipole moments.
For an overview over the effects of salts on dipole moments see [
91
].
Solutes in water
are of interest, because many chemical reactions are carried out
in water and this liquid influences the solutes and chemical reactivity greatly.
Hydrogen chloride HCl was investigated by Laasonen and Klein [
152
]. Several
AIMD simulations were performed with additional water molecules. Starting from
an HCl molecule in water, dissociation appeared forming H
3
O
+
and Cl
ions. Two
different configurations for the proton were reported: an H
3
O
+
ion and an H
5
O
3
ion.
An excellent overview of the solvated proton [
153
] and the hydroxyl ion in water
was published by Marx [
154
]. The solvated electron was also investigated exten-
sively from AIMD [
155
-
158
].
In a study from 2004, dimethylsulfoxide (DMSO) in water and its changing
dipole moment was investigated [
159
]. From the CPMD simulations the dipole
moment increase of DMSO from 3.97 D (isolated molecule [
160
]) to 7.39 D liquid
was observed. The temperature dependence of the dipole moment for isolated
DMSO was negligible; it increased from the geometry optimized value of 3.97 D
to 4.08 K at 319 K.
The solvent effects of uracil in water [
161
], ethene and ethanol in water [
162
], as
well as hydrogen in water [
163
] were discussed in detail elsewhere [
91
].
Solvent effects were found as well in the IR study of
N
-methylacetamide (NMA)
(
cis
and
trans
) in aqueous solution carried out by Gaigeot and coworkers in 2005
[
39
]. From geometry optimization of
N
-methylacetamide microsolvated with a few
water molecules, formation of bridges between the carbonyl functional group and
the amide group would be expected. However, no such arrangement was found in
the aqueous solution. A very noticeable effect of the solvent on the vibrational
density of states was that the amide I stretching motion exhibited a red-shift
(87 cm
1
for
trans
-NMA and 46-72 cm
1
for
cis
-NMA), whereas the amide II
3-38 cm
1
, respectively). In general,
solvent-solvent hydrogen bonds were observed to be energetically more favorable
than solute-solvent hydrogen bonds [
39
]. Whereas in the gas phase the neutral form
8-25 cm
1
was blue-shifted (
and
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