Evolutionary models have been calculated for Pop II stars of 0.5 to 1.0 { \mbox { \it M } _ { \odot } } from the pre-main–sequence to the lower part of the giant branch .
Rosseland opacities and radiative accelerations were calculated taking into account the concentration variations of 28 chemical species , including all species contributing to Rosseland opacities in the OPAL tables .
The effects of radiative accelerations , thermal diffusion and gravitational settling are included .
While models were calculated both for Z = 0.00017 and 0.0017 , we concentrate on models with Z = 0.00017 in this paper .
These are the first Pop II models calculated taking radiative acceleration into account .
It is shown that , at least in a 0.8 \mbox { \it M } _ { \odot } star , it is a better approximation not to let Fe diffuse than to calculate its gravitational settling without including the effects of g _ { { { \mbox { \scriptsize rad } } } } ( Fe ) .

In the absence of any turbulence outside of convection zones , the effects of atomic diffusion are large mainly for stars more massive than 0.7 { \mbox { \it M } _ { \odot } } .
Overabundances are expected in some stars with { { T _ { { { \mbox { \scriptsize eff } } } } } } { } \geq 6000 K. Most chemical species heavier than CNO are affected .
At 12 Gyr , overabundance factors may reach 10 in some cases ( e.g .
for Al or Ni ) while others are limited to 3 ( e.g .
for Fe ) .

The calculated surface abundances are compared to recent observations of abundances in globular clusters as well as to observations of Li in halo stars .
It is shown that , as in the case of Pop I stars , additional turbulence appears to be present .

Series of models with different assumptions about the strength of turbulence were then calculated .
One series minimizes the spread on the Li plateau while another was chosen with turbulence similar to that present in AmFm stars of Pop I .
Even when turbulence is adjusted to minimize the reduction of Li abundance , there remains a reduction by a factor of at least 1.6 from the original Li abundance .
Independent of the degree of turbulence in the outer regions , gravitational settling of He in the central region reduces the lifetime of Pop II stars by 4 to 7 % depending on the criterion used .
The effect on the age of the oldest clusters is discussed in an accompanying paper .

Just as in Pop I stars where only a fraction of stars , such as AmFm stars , have abundance anomalies , one should look for the possibility of abundance anomalies of metals in some Pop II turnoff stars , and not necessarily in all .
Expected abundance anomalies are calculated for 28 species and compared to observations of M92 as well as to Li observations in halo field stars .