Molecular oxygen tetramer (O2)4: Intermolecular interactions and implications for theεsolid phase

Abstract

Recent data have determined that the structure of the high-pressure phase of solid oxygen consists of clusters composed of four O 2 molecules. This finding has opened the question about the nature of the intermolecular interactions within the molecular oxygen tetramer. We use multiconfigurational ab initio calculations to obtain an adequate characterization of the ground singlet state of (O 2 ) 4 , which is compatible with the nonmagnetic character of the phase. In contrast to previous suggestions implying covalent bonding, we show that (O 2 ) 4 is a van der Waals-like cluster where exchange interactions preferentially stabilize the singlet state. Nevertheless, as the cluster shrinks, there is an extra stabilization due to many-body interactions, i.e., an incipient chemical bonding that just yields a softening of the repulsive wall. We show that these findings can be used to model the intra-and intercluster distances of -O 2 observed in the lower-pressure range and are consistent with inelastic x-ray measurements of O 2 K-edge excitations.

Collective spin 1 singlet phase in high-pressure oxygen

“…The approach should allow, even if at the approximate mean field level, for the presence of molecular spin whenever that should lower the total enthalpy. (ii) Describe the nature, stability, and optical properties of the resulting model S = 1 collective singlet state description of e 1 -O 2 , extending that in literature (12,13), particularly including quantum fluctuations. (iii) Predict the new phase diagram displaying a first-order e 1 -e 0 low temperature phase transition near 20 GPa, and a novel phase line predicting at high temperature a new critical point roughly at 30 GPa and 200 K inside the broad e-O 2 phase.…”

“…Our work has the following aims: (i) Provide first principles quantitative calculations of electronic and vibrational properties of same quality for both ǫ 0 -O 2 and ǫ 1 -O 2 , including Raman and IR vibrational frequencies and intensities that could be compared with experiment in both regimes. The approach should allow, even if at the approximate mean field level, for the presence of molecular spin whenever that should lower the total enthalpy; (ii) Describe the nature, stability, and optical properties of the resulting model S=1 collective singlet state description of ǫ 1 -O 2 , extending that in literature 12,13 , particularly including quantum fluctuations and ; (iii) Predict the new phase diagram displaying a first order ǫ 1 − ǫ 0 low temperature phase transition near 20 GPa, and a novel phase line predicting at high temperature a new critical point roughly at 30 GPa and 200 K inside the broad ǫ-O 2 phase.…”

“…An alternative, much more speculative picture insisting instead on a correlated state where O 2 retains its S=1 gas phase spin, and where the quartet of AF coupled sites yields a singlet ground state as the basic O 8 block of ǫ-O 2 , 12 provided no such successful predictions and had limited following so far -see however Ref. 13 .…”

“…Here we present theoretical results strongly connecting with existing vibrational and optical evidence, showing that this is true only above 20 GPa, whereas the S = 1 molecular state survives up to about 20 GPa. The e phase thus breaks up into two: a spinless e 0 (20−96 GPa), and another e 1 (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) where the molecules have S = 1 but possess only short-range antiferromagnetic correlations. A local spin liquid-like singlet ground state akin to some earlier proposals, and whose optical signature we identify in existing data, is proposed for this phase.…”

Rotational Spectrum and Conformational Analysis of N-Methyl-2-Aminoethanol: Insights into the Shape of Adrenergic Neurotransmitters

“…Although it has been shown that DFT methods are less accurate than for weakly bound systems (Bartolomei et al, 2011 , 2014 ), in this particular case, and concerning the relative energies between the gG'T and gG'G conformers, we can state that the B3LYP calculation (Δ E e = 1.22 kJ mol −1 ; Δ E 0 = 1.32 kJ mol −1 ) better reproduces the experimentally determined value of 1.9 (3) kJ mol −1 (Penn and Curl, 1971 ) with respect to the MP2 one (Δ E e = 0.46 kJ mol −1 ; Δ E 0 = 0.65 kJ mol −1 ). The same is true also for the methyl internal rotation barrier: the experimental value for the gG'T and g'GG conformers are 11.9 and 9.7 kJ mol −1 respectively, while the two values [B3LYP and MP2/6-311++G(d,p)] are 11.8/12.7 and 9.8/10.7 kJ mol −1 .…”