Recent content by sghan

Hello, in ice I have read that the average bond length of the hydrogen bond is about 2 Angstroms. This is roughly twice the O-H (covalent) bond length. My question is what really determines the length of the hydrogen bond? Why wouldn't the hydrogen be drawn closer to the next water...

What determines the crystal structure taken by metals? For example Sr has FCC and Ba BCC. The packing fraction is greater for FCC. However, due apparently to coordination number and number of "next nearest" neighbors, BCC is favored in the case of Barium despite its lower packing fraction...

Thanks DrDu! Does this mean, however, that BCC is simply a rhombohedral Bravais lattice? I do not see how BCC differs from the rhombohedral lattice.

And likewise, for FCC, you need a basis with 4 atoms (for BCC 2 atoms) in order span the lattice. Integer combinations of the FCC lattice vectors do not generate an FCC lattice. Yet FCC is Bravais, why?

On a related note, the FCC lattice is listed as one of the 14 Bravais lattices yet it seems to really be a case of SC with a 4-atom basis. Same for BCC: SC with 2-atom basis. Can someone explain why FCC and BC are considered Bravais when they clearly reduce to a simpler lattice, while...

Back to basics here! Do ions feel more or less coulombic attraction when dissolved in a polar solvent (compared to a less polar medium)? Does higher polarity of solvent increase the forces or decrease them? In other words, does the polarity of the solvent affect its dielectric constant...

Spherical Micelles of the surfactant DTAB, which has a cationic head, will turn into cylindrical micelles if the repulsion between the cationic heads can be reduced. I have read that adding salt (perhaps NaCl or NaBr) to this water/surfactant solution will reduce repulsion between the cations...

Hello, I am learning about using Free energy change /delta G to determine if a chemical reaction will occur spontaneously. /delta G = /delta H + T*/delta S. Now, enthalpy change can drive a reaction which leads to a decrease in entropy (multiple reactants => single product). My Question...

Thanks. Found the answer: in the program above, I'd have to put the subroutine in a module, then "use module" in the program. Only then does Present(x) work properly. If anyone wants to explain why this is necessary, I would appreciate it!

Hi all, When I use Present(x) to check for the presence of an optional variable, I am getting TRUE even when the subroutine call clearly does NOT contain the optional variable. See here the call to test_present(a,b): program options implicit none real*8 a,b real*8 c a =...