  Methods. We used the HIRES spectrograph on the Keck I telescope to acquire
high-resolution (R $\approx$ 70000) spectra with a high signal-to-noise ratio
(S/N $\approx$ 400 - 650 per pixel) of HIP 100963 and the Sun for a
differential abundance analysis. We measured the equivalent widths (EWs) of
iron lines to determine the stellar parameters by employing the differential
spectroscopic equilibrium. We determined the composition of volatile,
refractory, and neutron-capture elements through a differential abundance
analysis with respect to the Sun.
  Results. The stellar parameters we found are $T_{\rm{eff}}=5818 \pm 4$ K, log
$g = 4.49 \pm 0.01$ dex, $v_{t} = 1.03 \pm 0.01 $ $\rm{km\ {s}}^{-1}$ , and
[Fe/H] $ = -\ 0.003 \pm 0.004$ dex. These low errors allow us to compute a
precise mass ($1.03^{+0.02}_{-0.01}$ M$_{\odot}$) and age (2.0 $\pm$ 0.4 Gyr),
obtained using Yonsei-Yale isochrones. Using our [Y/Mg] ratio, we have
determined an age of $2.1 \pm 0.4$ Gyr, in agreement with the age computed
using isochrones. Our isochronal age also agrees with the age determined from
stellar activity (2.4 $\pm$ 0.3 Gyr). We study the abundance pattern with
condensation temperature ($\rm{T_{cond}}$) taking corrections by the GCE into
account. We show that the enhancements of neutron-capture elements are
explained by contributions from both the $s$- and $r$-process. The lithium
abundance follows the tight Li-age correlation seen in other solar twins.
  Conclusions. We confirm that HIP 100963 is a solar twin and demonstrate that
its abundance pattern is about solar after corrections for GCE. The star also
shows enrichment in $s-$ and $r$-process elements, as well as depletion in
lithium that is caused by stellar evolution.
