Density functional study of carbonic acid clusters

Density functional calculations on carbonic acid H2CO3 are extended to clus ters of up to five such units. The most stable forms are the linear, hydrog en-bonded analogs of the dimer with anti-anti orientation. We calculate str uctures and vibration frequencies, as well as the energy required to bend a nd stretch the linear isomers. Linear chains of up to similar to 20 units s hould be favored over ring structures, and they have a tensile strength rem iniscent of chains of water molecules. We also discuss planar, nonlinear st ructures as well as three-dimensional isomers. (C) 2000 American Institute of Physics. [S0021-9606(00)30615-8].